Troop transport in space battles

[asval]

I've come across troop transports in space battles that I can't target, I move a corvette along it's path and it fires at the transports but it wont kill it no matter how much it fires.

Is this a bug? if not, it's extremely annoying when the AI tries to break a blockade by using ground troops, I can't do anything but wait until they decide they've had enough and retreat.