I think I may have experimentally identified a condition for losing display of certain widgets.
I have seen this with v1.2.6, v2.0.0rc1 and now v2.0.0rc2.
Visable effects of the bug are that the button widgets cease being visible, but can be clicked on, Pop-up menus are similarly invisible but present and the ability to go from queue screen to upload screen is lost, but not the other way round. In preferances click boxes are present and the ticks are visible, but numeric entry boxes have invisible text. (Get the picture?) The server log window is blank until scrolled. It then works fine, however it is not repainted on window refresh.
This has been seen with various versions of wxGTK and the current version is 2.4.2 linked against GTK1.
I think one of the activations is completing a file. The temporary and saved directories are on the same filesystem, but different directories. Not sure if this will make any difference but it might do if there is a race condition going on.
Running on Linux, basically Gentoo. If you need me to test something then just ask.