After system crash I restarted Mint 17.1, finding:
gmbrc        8,5 kB
gmbrc.bak         0 byte
gmbrc.bak.20150909.xz         2,1 MB
gmbrc.error         0 byte
gmbrc.premove         3,1 MB

when my last backupped gmbrc is 12,4 MB
GMB says my collection is empty...

After restoring it, everything is fine.
What happened?


Sorry that happened.
I really do not know why this happens. It's probably too late, but if not do you have the modified time of these file, or at least of gmbrc.error ? (is it an old one or is it new from around the time of the crash)

If you're interested, here's basically how gmb saves : the data is saved in a new file gmbrc.new.PROCESS_ID, if any error happened while writing it is renamed to gmbrc.error, else the old gmbrc is renamed to .bak, and the new file is renamed to gmbrc.

In case you didn't know the gmbrc.bak.20150909.xz file is compressed, so even though it is only 2.1MB it is probably fine, and you can rename it to gmbrc without the need to decompress it, it will be decompressed as needed.