In working down an issue I was having I narrowed down this bug.
If a blueprint uses a parameter with a rarity (other than common) it will thus be unmarked, and changing that parameter no longer offers the rarity selection, forcing that rarity permanently. Only way to fix this is to place the blueprint and manually remove rarity from any instances and then re-create the blueprint. This applies to any copy-paste action just as well.
Above bp showing parameters of items or variables with rarity can't be changed any longer.
