Historical Rules · 25 January 2019
Rule 615.9
Official source text from the 25 January 2019 Rules release
Some effects generated by the resolution of a spell or ability prevent damage from a source of a player's choice with certain properties. When the source would deal damage, the shield rechecks the source's properties. If the properties no longer match, the damage isn't prevented or replaced and the shield isn't used up. See rule 609.7b.