Reply to Traktor's MIDI Sync sux (!?)

I would like to ask if any body of you noticed or experienced this. And hopefully has some explanation or even better solution because this has been driving me crazy for a while now!

Whenever I enable Traktor to send the MIDI Clock if I have any other controllers connected with mappings of features like VU meters, LED feedback of pots or even hot cue type LEDs, everything just glitches and the sound runs slow and pops. If I disable MIDI Clock the with rest of the mappings it work fine. My only guess is that Traktor can't handle so many MIDI messages, or that there is something wrong with my settings. Ableton seems to handle this fine..
Anybody else noticed this? And is there an issue with NI native controllers like the S2 or Z1 VU meters etc? Or do those run on a separate serial channel and not MIDI?