Hi Hartmut,
I recently built QTractor 0.4.5 on Jaunty, with LV2 support. I've since
upgraded to Karmic, but QTractor started and ran with no troubles. I
checked three LV2 plugins in QTractor, one each from linuxDSP, CALF, and
Invada. Only the linuxDSP plugins included their native GUI, the others
did not. My guess is that they do not adhere to the current standard.
HTH,
dp