I started a new play-through in version 1.03 and I'm double checking every battle. I've observed a weird behavior regarding deflection stacking which seems to be a bug (in the main section I asked, and people that replied agreed that it seems to be a bug). Please look at the reflex deflection of my character below (32 base + 5 from Fulvano's Glove):
During a fight, the following status effects were active on Eder:
Notice the +10 reflex deflection from "Blessed was Wengridth..." chant. I would expect Eder to have 32+5+10=47 reflex deflection since the sources are different: +5 from item, +10 from chant. But the resulting reflex deflection is only 32+10=42:
I am aware that deflections from the same source do not stack: +5 from one item and + 7 from another item gives only +7 total deflection. However, the sources of bonus deflection are different in the situation above: one comes from an item, while the other comes from a chant. This should be stacking.
Here is the save just before the fight.