Oh it wasn't actually my birthday, it was Audy's. :P
Yes, it's caused issues before. I'm using 1.92 which is supposed to be better than 1.95, but sometimes when expanding blocks and importing blocks, some tilesets are overwritten. I think it only happens when you're importing and not when expanding, though. And sometimes it doesn't even happen, I'm thinking it might have to do with importing not actually expanding the blocks and so some existing blocks in a different tileset are overwritten. Perhaps try expanding the blocks manually before you import them? It doesn't happen too often and it's easy to fix, and never caused any unfixable things for me, but keeping several backups when working with tilesets can help. Sometimes going back to a previous working ROM and doing the exact same tileset import/expansion will work just fine.