I have been able to move the column, adjust, move back, but haven't been able to do it today.

I don't know what was different before, but it may depend on what is selected in the tree panel, e.g. All Files, vs Files to Edit???

I can reproduce, added as: https://www.ventismedia.com/mantis/view.php?id=21952

For now you can move the column, adjust it and return it back to the last position.

I'm trying to clean up my database and it seems like whatever view I have of the Music folder (in the left tree pane of MM), for example "All Files", or "Files to Edit->Duplicate Titles", the rightmost column cannot be width-adjusted. For example, to make it larger.
If I grab the last column (Filename, in the Duplicate Titles case), and drag it left by one slot, so it's no longer the last column, its width is _still_ not adjustable.
What can I do to make that last field adjustable?