Strange perfomance decrease after ~40minutes

[submarine]

I'm experiencing the following behaviour:

If i set up a 1vs1 or 2vs2 test game with AAI or KAIK (from svn) my framrate sometimes drops almost immediately from ~60 to 1 ending in a total freeze of spring.

I tried to pause the game and press B to figure out which part of spring is suddenly consuming so much cpu power but the system does not react to any keys when this behaviour starts. The only thing I can (sometimes) do is Shift+Esc to end the game. I've never seen this happening in multiplayer games so far. so I think it is an AI (probably AAI issue). The first time I encountered that problem was after switching to spring 0.76b1. I have not added any potentially cpu demanding routines in the late/middle game for months (since I spent most of the time on the continent mpas that get precached, so those cannot be the reason)

Has any dev an idea?