Tribler slows down Windows GUI considerably

When running Tribler every Window/Program becomes very sluggish (only the graphical interface) , sometimes even the mousepointer lags.
For example, usually starting Task Manager is near instantaneous, when running Tribler, it sometimes takes one minute …
That being said, CPU isnt affected much, only about 30% CPU is used.
I am on Windows 8.1 x64.