Hi Thomas,
Thanks for the link with the VTK compilation process. Indeed VTK library is not yet available through usual linux installer software so you have to compile it yourself to start with. Hopefully i think it's much easier to do it on a Unix based system where compilers tools are always present, also linux users are somehow used to that :)
Also thanks for reporting the weird window duplication issue ! Just to be sure the problem does not come from a daemon plugin, can you try to temporary move all plugins from "plugins" folder elsewhere and test if the duplicated window still happen, i remember of some plugin potentially doing something wrong with VTK.
Cheers,
- Stephane