Well, I asked HR about it, and they were sort of tight lipped about why that happened (me being scheduled as GSA). I asked another Team Lead, who was surprised and concerned, and the shifts were supposed to be "fixed," but guess what? I'm still scheduled as GSA. Not happy. And of course, no mention of a raise or pay differential for those shifts. I'm beginning to really dislike my store, and I did not used to. They really need to get their act together.
Unless its a consistent pattern that meets or exceeds 50% of your shifts, you won't get a pay raise. If they think you're high potential and want to schedule you there once in a while, they can do that.
They might be testing you, but if you're giving them grief about it right away (I'd understand if its been ongoing for a while), they're going to think you aren't a team player, and will probably throw you to the curb. Just saying.