Comment 1 for bug 954444

I believe the first time around, when your entire desktop stopped responding, that was probably just the X server crashing as usual - UNetbootin doesn't do anything so fancy so as to trigger such a crash. As for your second run, I think that you just coincidentally happened to empty the trash right before the copy operation for a large file completed - if it had run out of space, then you would have seen an error message.