protect and unprotect a checkbox with a warning give me a erroneous behavior

Checking an unchecking a checkbox creates a protection "edit with warning", but unchecking does not erase this protection, as stated in the AppsScript code.

I reduced the problem to a minimum Sheet, with a minimum code. how to send this sheet? easier to see than to explain. or how to post images?

I suspect erroneous behaviour of cell protection of sheet data.

thanks for any help.