auto Locking files doesn't work properly, in the stream

Locking resources doesn't work properly. In the stream we defined several types of files that need to be auto-locked when edited. When editing the file for the first time, a lock dialog pops up. Locking, editing and delivering the file works oké. But then editing the file for a second time by the same user, the auto-lock dialog doesn't pop up.

The file can be edited without a lock. Sometimes first and second time do get the lock and the third doesn't, sometimes even the second time the file will not be locked.