I never noticed that prior to patch 3 but I cannot confirm this is a patch 3 consequence.

When engaging combat with the thralls on deck (prologue), it seems easier to aggro the two imps standing out of range.
On one occurence, after the thralls death, the imps were still out of visual range and my party was not able to end its turn / get out of combat.
Save (in combat) + reload used as a valid workaround.