WMA is not supported, mainly due to licensing reasons beyond the Windows platform. More info here. A previous build accidentally allowed WMA under certain conditions – see @danny’s explanation here.
The adding of empty albums sounds like a bug to me. Setting a flag for @mike to confirm.
That being said, WMA as a format is pretty much dead in the water. I appreciate that does not help your WMA library, but I can see you needing a conversion to something like FLAC sooner or later anyway.