I don't know what is causing this but it has something to do with how Explorer is handeling right clicks.

If you select a bunch of different files (like 100 or something), and want to access the context menu, it takes ages until the right click menu comes up - but then the Explorer window gets focus again (without any user interaction) and the menu disappears - i can only open the context menu when i select less files.

What can cause this behaviour? Context menu handlers (like WinRAR or sth.) or Windows itself? It is very annoying!