yeah mate mine were too but there must be something in the background thats fu*+$g it up ...... my only advice is try mediamonkey .....
...... why not delete all music off n900 .... then run the tracker-processes -r then choose one album that was messed up and run it through mediamonkey then add it to your n900 and see if it fixes it!
thats what i did so i ran all my albums through media monkey and all was good!