Could you check if you have filled the tag %albumartist%? If it is empty / non-existent then all the albums seem to come from the same artist "" ;-).
You can check this either with the extended tags of by showing an extra column in the file list that has the contents %albumartist".
Or you can set a filter
%albumartist% IS ""
which will display all files that have no albumartist yet.
You can then copy the artist to the albumartist tag with an action as described in the FAQ
/t/967/1