Render cache black "gaps" within clips

This has happened in both beta 1 and beta 2. It's a project that I began in 17 -- not a holdover from 16. This is reproduce-able in this project, even after multiple re-boots, etc.

I'm essentially working on a "slide show" kind of project with .jpg stills and dynamic zoom. On top of those I have a colored solid that's about 80% cropped from the top - i.e. a semitransparent colored bar across the bottom of the frame, and on top of all that there's a fusion composition that contains a text for each slide that does a movement into the frame at the beginning and out again at the end of each segment.

If I have Render Cache set to User, I will get render cache versions of each little 8-second stack of clips, but if it begins to render while the play head is inside the clip, there will be black frames and sections in the render cached version.

If I select the fusion composition for that broken part of the timeline while the play head is in a different area of the timeline, I can then delete render cache for "Selected clips...". I see the render indicator line go from blue to red to blue again as it re-renders the section, and everything is good after that.

I have not seen the black frames carried over into actual deliveries. I've successfully exported both h.265 and h.264 versions in mp4 wrappers with no black frames.

I haven't seen anything similar with Cache, but my timelines are very different, so that may be a factor.

This is continuing to be a problem, now in beta 9, and I’m pretty sure I can reproduce it at will.

It also happens in more conventional timelines, not just the slideshow.

See also: viewtopic.php?f=36&t=132312y