Why are bumps in painted nail polish?

either, because the nail polish is too thick, or old. most polishes do no, why not try, getting a new nail polish see if it does, mine don't bubble up, however some brands do because they may be cheap and not well made.

My Answer-

Yeah, if you put too much on, it's like paint and if you don't remove the excess it will clump up into a bubble and harden. It could also be because oxygen is trapped inside the paint, when it's put on your nails, it try's to escape but the polish hardens and doesn't allow it to go away. Thus the bubble.( It's like when you put a sticker on something, you have to press down evenly and make sure no air get's trapped under it or you get air pockets.) I recommend you stir the polish up more.

Now I'm just a guy (straight) and i never had experience with nail polish (haha), but I do know how to fix problems. Give me some props =).