As a mod-induced incident, it happens when there are two submarines in the scene that are "sharing" assets, such as an AI submarine and your own submarine, with the same conning tower, or deck crew, or guns, etc. That should have been "banished" from FotRSU quite a while ago. Not saying that it couldn't possibly be that, but that it shouldn't be that.
A 2nd way that happens is if something wonks the game's running information, which is why after you save, exit, come back in and load the Save, that things are back to normal. Generally speaking, the most common way that happens is by shelling out to Windows, whether accidental or purposeful. It used to be generally accepted practice to pause the game, shell-out to windows, say for the purpose of looking up a detailed map of a given area, and then coming back into the game, but that is NOT recommended. Do not leave the game at all for any reason. If you need to leave, Save the game, exit, do what you need to, reload the game and then the Save and continue.
Another way for that to occur is if you change the game "Mode". This just refers to Career, Single Missions, Quick Patrols, Multi-player Missions, and the Museum. Each of those "Modes" load a different set of files. If you run a Single Mission and then go directly into your Saved career from the Main Menu, you will have issues, some obvious to see, but mostly the little things, like you encountered. Generally speaking, if you use the Museum, and then try to load any other "Mode" of the game, it will not run at all. My suspicion of this behavior is insufficient buffer memory handling by the game. The devs just assumed no one would use the Menu the way it's layed-out, I guess. This is much more noticeable with the larger mods...
