This is an odd thing I noticed in a recent couple of SP games which looks like a bug, but I can't understand why it is occurring (or what I did to make it happen) since I don't remember seeing it when I first started playing Rebellion. In the case that it is a bug peculiar only to me, I can provide a savegame if need be.

If a Vasari Loyalist player researches Jump Stabilisation, the improvement (i.e. enemy hull damage drops to 15% and antimatter lost is 50%) is also applied to any enemies that are in a grav well which also contains a starbase belonging to that player. The enemy faction does not need to be Vasari Loyalist, the only requirement is that the starbase is Vasari Loyalist and Jump Stabilisation is researched. More bizarrely, the buff is apparently permanent, meaning that any units that have left a grav well containing such a starbase will continue to have jump destabilisation and will lose hull and antimatter each time the unit jumps again. The only way I have found to cancel the effect is to destroy the starbase.