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I understand there are a lot of quirks revolving around spell damage creatures (*rant redacted*) but I felt this one was bug worthy as the text on the cards is clearly incorrect.
Momentum says "Ignore all shield effects", and the sapphire charger's text says "shields are ignored", but both have the same effect, the creature has (or gains) the momentum ability. This ability remains on the creature when the creatures damage type becomes spell damage via SoW or if the creature had spell damage and is given momentum.
Both emerald shield and reflective shield have an effect (weirdly worded differently) that states "spells are reflected against your opponent" and "any damage from spells is reflected against your opponent" respectively. That is the effect of the shield.
However, as you can see in the above screenshot, neither the momentum-imbued psion or the quintessenced-Shard of wisdomed-sapphire charger are ignoring the opponent's shield effect.
I don't see a record of this as a non-bug, card text error, or other known/intended interaction. And it stands to reason if I cast momentum on any other creature and it ignores all shield effects, casting momentum on psion should give it that same ability. I also see nothing particularly OP about this interaction in either case. As playing the cards in a different order gives me an immortal charger who deals the same amount of physical damage that ignores the shield. Also if I cast momentum on any other creature it ignores all shields, with psion being the only exception, which definitely makes this look like an oversight in the order of operations more than an intended interaction.