If a monster sees you remove some piece of gear that grants a
resistance, it will remove that resistance from its list of remembered
resistances and be willing to try attacking you with that adtyp again.
This avoids the situation where you put on a ring of cold, get hit with
one cold attack, and then can remove it because all the monsters nearby
will permanently remember you as being cold resistant (but even after
this change a wily hero could still step into a niche and do it without
any monsters seeing, so trick them into thinking she's still cold
resistant...). The hero could still be resistant if there were multiple
sources to begin with, of course, but the monsters will test it and
learn that again if necessary.
It's a little weird that the monsters can recognize the intrinsic
granted by the item being removed, but they display knowledge of
unidentified (by the hero) objects in many other circumstances too, so I
hope it's forgivable in the pursuit of having them act more cleverly
about resuming previously-resisted attacks like this. Another approach
that avoids the gear recognition, blanking seenres on any gear change,
can result in odd situations like orcs treating their own cloaks as
potential sources of many different resistances, which also seems silly.
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