Shotcut 19.04.30 ; MacOsX 10.11
I managed to reproduce the problem I mentioned in the following thread
I have a project with 2 video tracks
On track V1 a clip without filter
On track V2 a color image “Black” on which I apply the filter “Mask: Simple shape”
In the video below the first 40 seconds show you the details of the 2 video tracks
I go to the “Keyframes” tab and adjust the “Horizontal” parameter so that the black circle is on the red.
Then I start the video with the “play” button on the player.
A little later, when the red circle has moved away from black, I stop reading with the “pause” button.
Note that the meter displays 01;26
I go to the parameter slider and move a little bit the mouse wheel (just one step)
A keyframe is created (at 01; 26) but note that the playhead has also shifted in the same time from one frame. It is now at 01; 27
When I go back on the parameter slider a new keyframe is created at 01; 27
See the screencapture below