Starting an app built with qt polls for harware changes exactly as xrandr does. This results in several freezes starting kde as well as starting a qt app. I guess the latter is implying the first one.

I found this out due to another intel bug which is not a qt problem. (Polling hardware with DisplayPort connected freezes X for about a second) Anyway this is not a proper solution, since hardware polling is slow in general and should be avoided.

This affects 5.3.1 on my ArchLiux system as well as qt 5 on an Ubuntu 14.04 Live System (I dont know the version exactly). Gtk and pure Xlib/xcb and command line applications do not show this behavior. Just to exclude genereal I/O problems out.

In more detail the debugger freezes X exactly at "QApplication a(argc, argv);"

Are you using XRRGetScreenResources() instead of XRRGetScreenResourcesCurrent()? This call is polling for changes. See http://www.x.org/releases/X11R7.6/doc/randrproto/randrproto.txt paragraph "RRGetScreenResources" and "RRGetScreenResourcesCurrent".