In the M10 release, multiple selects default to having the first item selected unless at least one option is "selected". This makes entering forms (including searching for bugs via bugzilla) which include more than one multiple select with no default values incredibly tedious.
Known issue; I think this is a duplicate...
Reassigning to Rod.
This has long since been fixed and it is a duplicate of some other bug, so to save sometime, I am marking it invalid.