Thematic enforcement of rules DO NOT APPLY. Ever.
Agreed, that if played in a serious competitive context, thematics are trumped by official rulings. And this should eliminate much of the bickering over the rules that some have found so taxing.
However, Descent can also be played in a light RPG context, in which thematics may have a small role to play in implementing house rules that enhance how a group enjoys playing. Even here, as long as everyone knows the rules ahead of time, and agrees upon them, much of the rules bickering can be eliminated.
I agree, thematics do NOT trump the rules. Another example of a debate I encountered on the same day as the Khorayt "shadow" debate was about gold and search cards. The heroes were under the impression that search items were allowed to be carried into new quests if not used. I showed them the rules and the section about search cards going back into the search deck at the end of each quest. They then argued that if not used, they should get double the gold. For example, they would get the 25 gold up front for finding a stamina potion, and then if they didn't use the stamina potion, they could sell it back for ANOTHER 25 gold, basically getting 50 gold for 1 stamina potion. I tried telling them that this was incorrect, but they were already mad that they couldn't keep their search items between quests so they weren't having any of my reasoning. I can't find anywhere in the rules where it says that their interpretation is correct, but then again I can't find anywhere where it specifically says they're wrong either. In my opinion, therein lies the problem with this game. It's far too open to interpretation and can easily be taken over by stronger personality types.