Lissajou deter display corrupt

[riban-bw]

After clicking around for a while, the stereo bar meters on the right of the Lissajou display is corrupt. The space between the top of the meters and top of screen / grey bars is populated with random video content. This may be horizontal coloured lines or different colour pixels. It is like the space is being rendered from undefined / uninitiated / random data.

I haven't figured out what workflow triggers this but it occurs fairly often. Probably some failure to clear the screen data before drawing the screen.

[martim01]

Can't reproduce this.