The latest JBL firmware is available for beta testing. You can get it here:
ftp://pubftp2pub2@ftp.ectaco.com/Lite-0.16.exe
This does appear to fix the bug that was introduced in v0.15g firmware. I've tested it by going back to the main menu and removing the batteries. The font size and the place in the book are remembered. I didn't see any other changes, but this is just supposed to be a bug fix.
This is considered to still be in beta testing, so install at your own risk.