I know, but with silent hunter games you just have to deal with things like that. Its one of the very minor bugs these games have.
For example, major bugs are:
unable to save the game (after hours on patrol)
unable to load saved games (corrupted due to saving in the wrong area, coast, near ships etc. especially sh3)
crash to desktop
CO2 rising when surfaced
etc etc.
Think of it like you have to refit your ocular from time to time
