I currently upgraded my kdenlive version to the new 16.08 but now the clip monitor and the project monitor don't work any more: they show only a grey panel.
I'm using Xubuntu 16.04, when starting kdenlive from command line it says:

Removing cache at "/home/dets/.cache/kdenlive-thumbs.kcache"
OpenGL vendor: "NVIDIA Corporation"
OpenGL renderer: "GeForce GTX 970/PCIe/SSE2"
OpenGL ARG_SYNC: true
OpenGL OpenGLES: false

Any ideas?