Fix Wallpaper selection window
(1) First of all I would suggest that you define a central directory where wallpaper could be stored and from that location it could be selected. This central wallpaper directory should be definable in the preference screen. Currently when you want to choose a new/different wallpaper you get by default directed in the local directory of the brain you are working in.
(2) The selection screen for wallpaper should make use of the existing OS file selection code to select the wallpaper, not the window selection screen that is apparently an own limited version created by the brain development team (have the impression that you created yourself a selection window that works the same way on all three operating systems). It would be better to reuse the 'default' file selection window of each operating system so you can see the thumbnails and pictures view before selecting it which in Version 6 in windows is not possible now. If you want to see which wallpaper you want to choose you have to go to the file-manager and use the thumbview. Advantage to re-use the code is that you don't have to write it yourself and don't have to test it as it is part of the basics of the file manager in each operating system you software is running.