You can have more than one install of AM. I would download 2.61 from the main page and try that and see if you get the same problem.
I run 2.6.2 and I generate my MAME list from the actual program and not via CLI and works fine for me.
It could be a bug, it could be user error, but I have not done it this way, so only offering what I would try.
Regards
Mark