Request.InputStream not complete after a checkbox postback

I'm having a problem with a ASPX page of our production application that throws a lot of randomly weirds exceptions, as I explain now:

1.- A user write a value on an AutoPostBack TextBox (mnt_embarque). We received this Request.InputStream information:

EVENTTARGET=mnt_embarque&__EVENTARGUMENT=&__LASTFOCUS=&__VIEWSTATEGUID=4bcf3d2c-2dcf-4264-9743-5c32cf01cd79&__VIEWSTATE=&sfm_buscar%24alto_ventana=&sfm_importar%24alto_ventana=&sfm_exportar%24alto_ventana=&sfm_detalle%24alto_ventana=&sfm_configuracion_factores%24alto_ventana=&sfm_declaraciones_de_ingreso%24alto_ventana=&txt_carpeta=%5B27369%5D-&mnt_embarque=2&fps_gasto_flete_nacional%24data=%253Croot%253E%253Cdata%253E%253C%252Fdata%253E%253Cstate%253E%253Cchartinfo%253E%253C%252Fchartinfo%253E%253Ccolinfo%253E%253C%252Fcolinfo%253E%253Crowinfo%253E%253C%252Frowinfo%253E%253Cselection%253E%253C%252Fselection%253E%253Ccellinfo%253E%253C%252Fcellinfo%253E%253Cactiverow%253E-1%253C%252Factiverow%253E%253Cactivecolumn%253E-1%253C%252Factivecolumn%253E%253C%252Fstate%253E%253Cactivespread%253E%253C%252Factivespread%253E%253Cactivechild%253E%253C%252Factivechild%253E%253Cscrollleft%253E0%253C%252Fscrollleft%253E%253Cscrolltop%253E0%253C%252Fscrolltop%253E%253C%252Froot%253E&fps_gasto_flete_nacional%24extender=&fps_gasto_internacion_peso%24data=%253Croot%253E%253Cdata%253E%253C%252Fdata%253E%253Cstate%253E%253Cchartinfo%253E%253C%252Fchartinfo%253E%253Ccolinfo%253E%253C%252Fcolinfo%253E%253Crowinfo%253E%253C%252Frowinfo%253E%253Cselection%253E%253C%252Fselection%253E%253Ccellinfo%253E%253C%252Fcellinfo%253E%253Cactiverow%253E-1%253C%252Factiverow%253E%253Cactivecolumn%253E-1%253C%252Factivecolumn%253E%253C%252Fstate%253E%253Cactivespread%253E%253C%252Factivespread%253E%253Cactivechild%253E%253C%252Factivechild%253E%253Cscrollleft%253E0%253C%252Fscrollleft%253E%253Cscrolltop%253E0%253C%252Fscrolltop%253E%253C%252Froot%253E&fps_gasto_internacion_peso%24extender=&hf_decimales_CantidadValorTotal=2%7C8%7C2&hf_EstadoPagina=modificar&hf_validar=NO&hf_IDInterno=0&hf_TituloPagina=Costeo+de+mercaderias&hf_mensaje_eliminar_contenedor=Se+recuerda+que+al+eliminar+un+contenedor%2C+tambi%C3%A9n+ser%C3%A1+eliminado+de+los+productos.%5Cn+%C2%BFDesea+continuar%3F&hf_mensaje_marca_contenedor_incorrecto=La+sigla+del+contenedor+ingresado+es+incorrecto%2C+favor+revisar+e+ingresar+nuevamente.&hf_mensaje_sin_contenedores_para_asociar=No+existen+contenedores+para+asociar+al+producto+seleccionado.&hf_pnl_gastos_flete_display=none&hf_pnl_gastos_internacion_display=none&hf_mensaje_confirmacion_copiado=%C2%BFDesea+copiar+el+contenido+ingresado%2C+en+las+filas+continuas%3F

2.- A user do uncheck an AutoPostBack checkbox a few seconds later (chk_cerrar). We received this Request.InputStream information:

EVENTTARGET=chk_cerrar&__EVENTARGUMENT=&__LASTFOCUS=&__VIEWSTATEGUID=4bcf3d2c-2dcf-4264-9743-5c32cf01cd79&__VIEWSTATE=&sfm_buscar%24alto_ventana=&sfm_importar%24alto_ventana=&sfm_exportar%24alto_ventana=&sfm_detalle%24alto_ventana=&sfm_configuracion_factores%24alto_ventana=&sfm_declaraciones_de_ingreso%24alto_ventana=&fps_gasto_flete_nacional%24ctl09=&fps_gasto_flete_nacional%24ValidatorHold-1=&fps_gasto_flete_nacional%24ctl12=&fps_gasto_flete_nacional%24ctl14=&fps_gasto_flete_nacional%24data=&fps_gasto_flete_nacional%24extender=

3.- A user do click a button a few seconds later (btn_aceptar). We received this Request.InputStream information:

EVENTTARGET=btn_aceptar&__EVENTARGUMENT=&__LASTFOCUS=&__VIEWSTATEGUID=4bcf3d2c-2dcf-4264-9743-5c32cf01cd79&__VIEWSTATE=&sfm_buscar%24alto_ventana=&sfm_importar%24alto_ventana=&sfm_exportar%24alto_ventana=&sfm_detalle%24alto_ventana=&sfm_configuracion_factores%24alto_ventana=&sfm_declaraciones_de_ingreso%24alto_ventana=&fch_embarque%24fch_embarque_texto_fecha=15-07-2015&fch_tc_contable%24fch_tc_contable_texto_fecha=15-07-2015&fch_iva%24fch_iva_texto_fecha=21-08-2015&mnt_tc_especial=0.00&cmb_mes_tc_aduanero=08&mnt_ano_tc_aduanero=2015&mnt_cantidad_cajas_carnes=0&cmb_estado=80509&rdl_peso_valor=por_valor&fps_gasto_flete_nacional%24ctl09=&fps_gasto_flete_nacional%24ValidatorHold-1=&fps_gasto_flete_nacional%24ctl12=&fps_gasto_flete_nacional%24ctl14=&fps_gasto_flete_nacional%24data=%253Croot%253E%253Cdata%253E%253C%252Fdata%253E%253Cstate%253E%253Cchartinfo%253E%253C%252Fchartinfo%253E%253Ccolinfo%253E%253C%252Fcolinfo%253E%253Crowinfo%253E%253C%252Frowinfo%253E%253Cselection%253E%253C%252Fselection%253E%253Ccellinfo%253E%253C%252Fcellinfo%253E%253Cactiverow%253E-1%253C%252Factiverow%253E%253Cactivecolumn%253E-1%253C%252Factivecolumn%253E%253C%252Fstate%253E%253Cactivespread%253E%253C%252Factivespread%253E%253Cactivechild%253E%253C%252Factivechild%253E%253Cscrollleft%253E0%253C%252Fscrollleft%253E%253Cscrolltop%253E0%253C%252Fscrolltop%253E%253C%252Froot%253E&fps_gasto_flete_nacional%24extender=&fps_gasto_internacion_peso%243%2C0=on&fps_gasto_internacion_peso%24ValidatorHold-1=&fps_gasto_internacion_peso%24ctl11=&fps_gasto_internacion_peso%24ctl13=&fps_gasto_internacion_peso%24ctl15=&fps_gasto_internacion_peso%24ctl17=&fps_gasto_internacion_peso%24ctl19=&fps_gasto_internacion_peso%24ctl21=&fps_gasto_internacion_peso%24ctl23=&fps_gasto_internacion_peso%24ctl25=&fps_gasto_internacion_peso%24ctl27=&fps_gasto_internacion_peso%24ctl30=&fps_gasto_internacion_peso%24ctl32=&fps_gasto_internacion_peso%24ctl35=&fps_gasto_internacion_peso%24ctl37=&fps_gasto_internacion_peso%24ctl40=&fps_gasto_internacion_peso%24ctl42=&fps_gasto_internacion_peso%24data=%253Croot%253E%253Cdata%253E%253C%252Fdata%253E%253Cstate%253E%253Cchartinfo%253E%253C%252Fchartinfo%253E%253Ccolinfo%253E%253C%252Fcolinfo%253E%253Crowinfo%253E%253C%252Frowinfo%253E%253Cselection%253E%253C%252Fselection%253E%253Ccellinfo%253E%253C%252Fcellinfo%253E%253Cactiverow%253E-1%253C%252Factiverow%253E%253Cactivecolumn%253E-1%253C%252Factivecolumn%253E%253C%252Fstate%253E%253Cactivespread%253E%253C%252Factivespread%253E%253Cactivechild%253E%253C%252Factivechild%253E%253Cscrollleft%253E0%253C%252Fscrollleft%253E%253Cscrolltop%253E0%253C%252Fscrolltop%253E%253C%252Froot%253E&fps_gasto_internacion_peso%24extender=&hf_decimales_CantidadValorTotal=&hf_EstadoPagina=&hf_validar=NO&hf_IDInterno=27396&hf_TituloPagina=&hf_mensaje_eliminar_contenedor=&hf_mensaje_marca_contenedor_incorrecto=&hf_mensaje_sin_contenedores_para_asociar=&hf_pnl_gastos_flete_display=none&hf_pnl_gastos_internacion_display=none&hf_mensaje_confirmacion_copiado=

All InputStream information has been captured on the Global_asax.AcquireRequestState event. As i can see, after the postback of the checkbox, the InputStream has lot almost all information that the user has been working on. This problem happens pretty often.

What may be causing this problem? I really appreciate your help on this difficult situation.