If I drag a few album files that have previously been tagged back into the left hand pane and press lookup or scan on the group, Picard always updates some of the albums & always the same albums. The remaining albums always remain unchanged.
When I look deeper, it is always (and only) the WMA files that get updated, not the album art. If I repeat the process a minute later, I get the same thing and I’ve noticed that nothing in the Original Value column has been altered from the data displayed in the New Value column. Further...
I have only tried WMA files as they are all that I have at the moment. Here’s my exact steps to produce the problem:

1. Drag 2x of the previously tagged offending WMA ripped albums into the left pane.
2. Picard does its stuff and they appear as updated in the right hand pane, but no tags at all have been altered anywhere and nothing is highlighted in any way.
3. I save both albums, and the asterix indicating the updated info disappears.
4. I drag both albums individually back into the left pane & hit Cluster.
5. I then highlight Clusters (2) and press Lookup.
6. After a few seconds the albums show as again being updated in the right hand pane. Again nothing has changed and nothing is highlighted on either the Album headers or the individual tracks.

The behavior is identical in V 2.0.4.