asp.net gridview checkboxes are unchecked randomly

I have a problem with checkboxes in my gridview. The gridview is bound to a sql database. Each row has multiple columns and a checkbox which is also bound to the database (column „is Checked“ it is defined as „bit" in sql).
If the checkbox is checked the row gets updated in the database („isChecked“ value set to 1) and the gridview is refreshed. Everything works fine until after a while all checkboxes on the current page index loose the checked state. The page size is 100 rows. If I look in the database I see that all 100 rows are updated to „isChecked“ = 0. This happens totally random. I tried 1000 times to adjust this behavior but with no luck.

It seems to be that it only happens on a special constellation. I do some sorting on the gridview and also refill the gridview by a „Refresh“ Button some times.

Does anybody know such problem?