Example: I FREEZE my opponent, who steals the card with DUCK. He then uses FREEZE on my char. I then PURGE my frozen char, but the effect doesn't go away. It says PURGE works on "enemy controlled cards." I would argue: 1) When the enemy uses a stolen card, he is controlling it. So, I should be able to PURGE it. Otherwise, change "controlled" to "owned", like in MTG. 2) It's counter intuitive that I cannot purge an effect he placed, even if the card was stolen from me. 3) If it is working as intended, I cannot even know if effect was in fact placed by the card he stole, or one of his own cards. Neither can he, probably. 4) If it's not working as intended, DUCK is stronger than intended.
A very similar situation happened to me today; my human wizard tried to Freeze the enemy dwarf, but the dwarf blocked it with Duck, and froze my wizard. My priest tried to Purge the wizard, but the card didn't go away. I thought that is must have considered it my own card, however... The next turn I forgot about the freeze and tried to move my wizard anyway, and, to my surprise, my wizard was able to move with Run, despite having encumber 3. (Release 1.8)
I would just like to mention that this si still the case. A character used "duck" against "bad luck" then cast "bad luck" on my character, i was unable to purge it. I noticed another thread mentioning the un-purged effect, could just be a graphical bug. I have no way of knowing trhis, since i won the turn after and was not able to tell if "bad luck" was in effect after the purge was cast.