I can't seem to find out what you mean...
What is broken?
It not getting XP in invulnerable
It getting XP in invulnerable
It giving XP before invulnerable
It giving XP after invulnerable
I haven't played in a long time so not sure what it does currently
Ok, to clarify this is when fight against the AR titan, before the AR titan has taken any levels of "Unyielding Will" everything seems to be working fine.
Once it has a level of "Unyielding Will" this is where things start to go a bit weird, just as I'm about to kill a lone AR titan, "Unyielding Will" activates just as it should, I've got my fleet still in the gravity well (without jumping out of it) and keep making the AR titan chase me around until "Unyielding Will" wears of and it finally dies, my titan and capital ships that survive are still at the same xp amount at the end of the battle as they were at the start of the battle.
Thus the xp bug seems to be within the execution (codewise) of the "Unyielding Will" ability.
Hope that clears up any confusion for you.