[Cin] Compositor screen stays empty after playing with video fader

[mnieuw at zap.a2000.nl]

Creating a small 1080p video with one title track op top and four short
movies, the title track did not yet have any titles in it.
I was trying to play with the audio and video fader in the patch panel.

Editing mode was drag/drop, keyframe while editing generation not
enabled. The four videos are time shifted so they play with an empty
second in between. Initially this works fine.

Audio fader works fine, it shows as horizontal stripes in the patchbay
with a vertical bar through it. If fader view is enabled (3 on the kbd)
you see it moving with the fader.
The video fader only shows horizontal stripes, not the vertical bar.
Neither does the fader view show a horizontal line.
After some clicking on the video fader the vertical bar appeared, as
the the horizontal line in the video track. The compositor window went
black and stays black, whatever I try; sound is normal. If the video is
not playing, then you can make the "safe regions" appear/disappear
(F10), so it seems the compositor itself is OK. 
The video fader only seems to know values 1 and 0, more a switch that a
fader...

I have had this twice in a row, after starting a new project each time.

Disable, then enabling a video track in the patchbay makes no
difference.

CinGG AppImage was 2022-04, machine AMD 5700G, video mode X11-openGL
(just X11 same problem), hardware accel not working. Exiting and
reloading CinGG make no difference, the only way to get the compositor
back is start a new project; therefore it must be a stored setting
somewhere. 
In the project .xml file the MUTEAUTOs and FADEAUTOS settings look the
same for audio and video, else I don know what to look for.

Obviously I am doing something wrong, any suggestions?

MatN