The problem basically is that your opponents' creatures will not hit through Dimensional Shield, even when Antimattered. However, your creatures
do. In pvp this creates weird inconsistencies that solve themselves by undo-ing the healing, so I assume the bug is that the creatures on your side of the field can hit through Dimensional Shield when Antimattered.
Spoiler for proof:
Setup: Dims on both sides, both sides have 4 damage done to them and an antimattered Phase Spider.
Phase Spider hits through Dimensional shield according to the one attacking with it, but you can still see the miss from the other side's perspective.
Same happens for the other player, when this player ends their actions the healing done by the Phase Spider hitting through is suddenly undone.
