Can you check if a newest build fixes the problem? I've made a few improvements in playback feature between builds 6.1.7-6.1.9 so I wouldn't be too surprised if it's already fixed.

Other than that, try changing options in View -> Preferences -> Media.

It's also possible that QCD is not properly registered in a system for M3U file types, in which case reinstalling or re-registering file types might help.

Andrei