I first brought this bug up as #2 in my bug report for the v19.08 beta here.
In @Earlybite’s thread about the Keyframe timeline here, I found out that this bug is not limited to filters with rectangle control as I found it out with the Rotate and Scale filter. It may also affect other filters. @shotcut said in Earlybite’s thread that his fix covered the bug I brought up but testing out the 19.09.14 release it turns out that the fix only covered what Earlybite reported. So that’s why I made this separate thread.
The bug basically is that if you take a clip that is in the timeline that has keyframes already set but decide to then extend the clip and add keyframes to that extended section then those new keyframes will not work.
Here is a new demo I made with the 19.09.14 release this time with the Rotate and Scale filter.