I select many directories, right click and choose "Mp3tag". All the files from them are loaded into the program, but the directory displayed in main window title and on the left is the last directory in the list. I don't think this behaviour is logic and could be even misleading.
Do you have a suggestion on how to improve this?
The ideas here will be a little more wider than the discussed issue, however, they stay on the topic.
My suggestion would be to get rid of the dualism in directory management in Mp3tag, which presumably comes from its old times. I mean, that on the one hand we have a current working directory (one) and on the other - we can add as many directories as we want (many).
Despite that, the current way of working with files using a list of independent files is, IMHO, the best. You can add directories from whatever parts of your file system, you can delete files from the list. So actually there is no current working directory. The problem is in the naming conventions and the logic that comes out from them. What "Change directory... [Change current working directory]" button does is that it conveniently starts a new list from some directory. Remember, you wrote that you do not plan to add a folder tree, because this would tie the file list to the current folder (the last part is my understanding of why you did so).
So I think that Mp3tag should remember the whole list of directories (ideally - the list of files, but that would be too slow). Current version remembers the last directory only.
Now on what the title and the Directory combo should show. I think that the Directory combo box is the most inconvenient part of the program right now. It is situated among tag editing fields, but it doesn't belong to this group. It remembers the list of recently loaded directories and acts like "Change directory..." button. The width of the panel often doesn't allow to see the endings of the directories in the list. My suggestion would be to move the feature of opening the recent directories to a drop-down list of the "Change directory" button (like the list of actions when I click the arrow near the Actions button).
If the above suggestions are implemented, there role of the Directory combo should be changed (invented again). I'd suggest it to be the path or better the last directory in the path of the currently selected file (thus keeping the name Directory). There's a lot that might be done with it, but is a separate topic to discuss.
The title should try to give an idea of what directories are opened. It should start with the names (not pathes, that's too long) of the root-most directories and list them while there's space in the title bar.
"Change to upper directory" would be enabled only when some file is selected.
Thank you for reading.