It seems like certain filesystems are not bootable. I don't know what was the exact issue, but I couldn't boot from 4Gb flash disk until I partitioned it to 1Gb (not 4Gb by default), FAT16 (not FAT32 by default) and with some small sector size (not 32k).
Anonymous
I "reproduced the problem", at least with GParted. It requires Fat 16. Wasted a couple hours before figuring that out. It would be nice if that was documented both here and as part of GParted Live.