@Marindor ; Here are the screenshots as i promised.
This is 2nd round, my archer and the orcs moved and ended their turns. My treants' turn now. They hit the orcs and apply debuff on them.
This is the start of the 3rd turn (Don't get confused it says 2.Round in the initiative bar, it is wrong. Must be another bug. You can see at the right the next round will be round 4). The Daze ability weakens the target for the "current" round. So the effect must have been worn off in the 3rd round. It seems to be still active though, both orcs have the heart shaped debuff icon on them. (As i said before, the initiative bar isn't bugged, everything is ok there, no debuff icons)
But it only "seems" so. They are not weakened in fact. Here is again the orcs' turn and they hit just normally, without any debuff. (-90% is just the regular defense bonus of Treant II against light melee.)