A bit more info that may hopefully help others who come upon the same situation.
I went back to a save before the battle of the grove and basically repeated the smae combat. Knock out Minthara and kill all the goblins. I started to loot the corpses when the action was interrupted by Zevlor's victory speech.
It then occurred to me that the victory speech did not trigger the prevous time, and I assume this is what blocks the termination of the quests.
Perhaps I started to loot too quickly. (I always have a bit of lag when the scene changes ) and screwed up a sequence to trigger that speech. So anyway, it looks like it may be caused by some kind of slowness of my system, but certainly not by the use of Gale as my Tav.
