Rejected then accepted

Idk what's going on with this year's admission cycle but I had a weird experience with one school. I was rejected by a Master's program in January. Just rejection, no waitlist or anything. Then in late May the department chair sent me an email saying that I got in. I ended up not going cause I have already committed to another school but...if they'd let me know earlier I would have gone to that one. Still, I don't think it's a professional behaviour. What do you think, is this a common thing?