Could I get penalized for this at work?

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At my job, they use a website service to request time off, trade shifts, drop shifts, send messages, check schedule, and so on... I've been dropping quite a few shifts over the past 3 months, maybe about 2 weeks worth. This is due to stress and vacation planning around my girl's job schedule. Now when you drop a shift at my job, that doesn't mean you're calling out, that means you're putting it on a board for someone else who doesn't have 40 hours to pick it up for you. If they take it, great you're off, if not, well you gotta go to work. So u figure u can't get in trouble for that right? Ur not calling out. But a supervisor came up to me today and asked what all the dropping was about and if everything was ok, I explained it to him and he said oh ok its no problem, he thought the schedule wasn't working for me... However that kinda scared me right there, what do u think about this?