Can anyone confirm this behaivour on 5.1.2, please?
I drop a clip into a workline, Apple J and change the speed to 150%. I let a little bit of this render, test it, and decide it's not fast enough. Then I select the clip again, change the speed to 200%. The rendered bit does not change to show that it needs rerendering.
I render what's left to render and play it. The first part of the clip that didn't need a rerender plays at 150%, the second part, which I just rendered, plays at 200%. The workaround I'm using is to set the reverse button to force unrender, then reset to the correct settings, and re render.