Difficult to say, but certainly not too many sub folders or something ...
If that "Folder" file which is showing doesn't have an extension, please rename it to Folder.jpg and see whether it makes a difference.
With such a structure, I can imagine that things are not in "balance" somehow, and at (me) working through the structure, unexpected things happen. So, in general there is a deepest level of where the track data is, and the only thing allowed under that (deeper again) is coverart folders. Thus, suppose there's track data in your Anne-Sophie folder (I can't see that), things will go wrong because you also have album folders in that same folder.
Otherwise I really don't know.
Since you know where you have this issue, and it seems to be at one place only (?), it would be great if you can find yourself what causes this. After that I can adjust the program to that, unless you do something "illegal" (like the before example with track data and album folders mixed).
I know, not much helpful, apart maybe from the fact that what I see is just allowed.
This also happens if I try to leave that directory by typing an artist's name with the keyboard.
I don't think that can happen (the "leaving"). So, that it goes wrong I sure believe, but this must always be something in the chosen folder folder itself. Now, if you recognize this is the same problem, it may be easier to drill down to the folder having the issue (if one (only) at all).
So, if you see E:\Music I\Classical\Bach\ at the bottom, and you type "best of", only the \Bach\ structure (all the way down) will be examined, and not e.g. \Antonio Vivaldi\. Unless :
Unless you mean you type c:\Music I\Chuck at the bottom, and force to "leave" the Bach structure by this means. But if so, does this go wrong only at clicking Search ? or also without clicking Search ?
I hope I am clear a bit ...
I hope you can find what causes this !
Peter
PS: When does that cyan color at the top of the form emerge ? It indicates somethingis wrong (it should be transparent).