So I'm back from a single player game. I was TEC Loyalist fighting the last remaining AI, an Advent Rebel faction. Their level 10 Eradica Titan is by itself in one of my systems after my double starbases wreck the rest of the fleet. My level 10 Ankylon Titan, backed up by all of the level 10 Capital ships I can support and a mass of inconsequential frigates is also in the system by this time, so I order them all to attack the Advent Titan. Things are going well until the Advent Titan is almost destroyed and it pops it's ultimate ability (I forget the name), which gives it invulnerability, increased anti-matter regeneration, and reduced ability cool-down. I figure it's no problem, I'll just wait until the duration is over. Problem is, it never stops being invulnerable. 3 minutes later, I'm convinced that the ability will end any second now. 2 minutes after that, I'm wondering if the massive reduction in ability cool-down is also applied to the ability just used, resulting in the Titan able to use this ability again immediately after it ends.
TL;DR: Advent Rebel Titan invulnerability ability appears to have infinite duration. Wondering if this is a bug and, if not, how to deal with it.