Q: FCPX whites and custom colour generator

I'm having a problem with the colour generators in FCPX not sticking and becoming transparent or disabling themselves.

For example, using the whites generator as background for some footage, it will work initially then fail to render as white (or the custom colour selected). Effectively it disables itself even though it is not disabled, becoming black instead.

Has anyone else had this problem? Does anyone have a solution? Thanks