This has a negative effect in that, firstly, it can make early-game weapons useless against critters with certain feat combinations unless you go out of your way to design a model specifically for fighting that critter, and secondly, since the feat description fails to make it clear that hitpoint modifiers from unit feats still count, there's a decent chance that a player who has only read the feat description will try to fight such a critter with units that can't beat it and only learn how the mechanic actually works when they look into why their troops got massacred. Thirdly, players have to add up all the hitpoint modifiers from the unit feats to figure out if a model actually beats the critter's Absorption, and in order to do that properly players have to know that combat modifiers compound each other's effects in the game's combat engine, which is another thing about the feat that may trip up new players.
For another related bug or undocumented feature, I noticed that my air bombardments were still sometimes scoring hits on critters with Absorption even though they didn't have enough attack power to beat it. Most attacks were nullified, but for a small portion, the text about the attack being nullified was missing from the combat log and the attack went through, even though the base attack and base defense were identical to nullified attacks. If some too-weak attacks getting through is an intended mechanic, it should be mentioned in the feat description.
