Sometimes characters disappear when saving a file

[niente0]

Hi, it often happens to me that when saving a file while comparing it to another one some parts of code disappear. It can be an "end if" (ASP Classic) at the end of a block of code, or a } (closing bracket in Javascript). If I re-insert it in the same place where it disappeared, it vanishes again when saving. I think it's a serious bug that should be fixed.
It is somehow difficult to replicate this error, I tried to create test files with no success, I'll try again.