Oh dear, yeah that similar lock up happened to me once and I could never quite reproduce it. Quite the fickle thing!
Didn't encounter the fire flower problem but bugs do have quite the habit of never appearing until launched. Won't really be pursuing the project any further, was pretty much for a bit of fun and seeing just how difficult making a fleshed out platformer like this is with GB Studio. (Very much so as it turns out!)
Sad to hear the music wasn't quite your cuppa, but glad at least the sprite art was.