"Use Render Cached Images" w/retimed clips = Bad Renders

When rendering a timeline using the "Premiere XML" delivery preset, and you have clips in the timeline which have been retimed and have been render cached (e.g. cached Optical Flow/Speed Warps), and then you render the timeline with "Use Render Cached Images" enabled, the resulting renders of the retimed clips not only contain "baked in" optical flow frames, but also incorrectly repeated frames.

After doing some tests, it seems that the issue only occurs if you retime a clip faster than 100% in the Resolve timeline.

Here's an example of a 23.976 clip, in a 23.976 timeline, retimed to 125%, and Optical Flow/Speed Warp enabled.

No Render Cache: https://d.pr/v/xtl6yo

Use Render Cache: https://d.pr/v/6vMuXB

You can see that the "Use Render Cache" version has repeated frames, as well as optical flow frames, neither of which should occur if you're rendering the timeline for a Premiere XML roundtrip, since all the clips are supposed to be rendered at their original frame-rates.

The "No Render Cache" version is how the clip should be rendered.

The obvious workaround is to render the entire timeline with "Use Render Cached Images" turned off, but is a huge workflow slowdown, because if you have a timeline containing render intensive effects on clips that aren't retimed, then you have to waste time re-rendering stuff that has already been render cached.

For roundtrip delivery presets, the render cache should always be ignored for all speed changed clips, because the host application you're roundtripping to is supposed to be handling the retiming processes itself, based on the roundtrip XML/AAF that Resolve writes out when using these presets.

This issue has existed in Resolve since at least v14 (when I started noticing it), and continues to occur in 17.1B (Build 3)