I added some AI code, which resulted in some ships moving about. I ended up with three different empires' fleets in one system. When mousing over the top two, things were fine. But the 3rd / bottom fleet does not respond visually to being moused over, and doesn't respont to clicks.
http://home.cogeco.ca/~toppingwebspace4/FO/3rd_Fleet_Not_Mouseoverable.png
save with 5 empires' fleets in one system
Logged In: YES
user_id=913462
Originator: YES
The 4th and 5th fleet icons (each for a different empire) are also nonresponsive to mouseovers / clicks.
Logged In: YES
user_id=913462
Originator: YES
Fixed in Subversion.