Incorrect interaction between Prevent Damage and Shield Counters

Machine

I have a Swans of Bryn Argoll in play (4/3 creature with Flying, Prevent Damage, and Defender). I gave it Shield 2 by paying the gift cost of Perch Protection. Whenever the Swans block an opposing creature, it loses one of its shield counters. This should NOT happen, as the Swans have prevent damage.

Xibvert

I wouldn't say this is for sure incorrect. Shield counters talk about when an opposing source would make the card take damage. So it sounds like it might be meant to trigger before the point that or prevent damage would kick in. It's one of those things where it's a little fuzzy because of the game not having comprehensive rules to clarify exactly how everything works. I could see them going either way on this depending on what they want the interaction to be.

There's already scenarios like a creature with prevent damage blocking a creature with trample. In that case what's counted as excess damage and how much goes to the blocker is obviously being decided before the damage is prevented otherwise there wouldn't be any excess damage to hit the player with.