I've encountered some unexpected behavior in both PitBull_Aura and PitBull_AltAura. (Yes, the exact same behavior occurs with either module enabled.)
For the Player unit frame, frame debuff highlighting works while I'm in combat, but the frame highlight is cleared immediately when I leave combat, even if I still have the debuff. If I target myself, the Target unit frame never seems to receive debuff highlighting. Oddly, the Target-of-Target unit frame does get the frame highlight and keeps it until the debuff fades or is dispelled.
Edit: Due to the many recent changes to PitBull, I completely uninstalled it and all its modules, and deleted all its SavedVariables. The same bad behavior appears on a completely fresh install of r60526.
You need, IIRC, buffs or debuffs enabled to get Frame highlighting to work for any given unit frame.
Buffs and debuffs are both enabled on the player, target, and target-of-target frames. In fact, except for the position of buffs and number displayed, they have the exact same PitBull_Aura settings. The issue is that the player frame is correctly highlighted when I get a debuff, but the highlight disappears prematurely when I leave combat.