Make tracks taller only works in V1

After inserting a video to track V1, I added another track A1, but when I right click the A1 track and select Make tracks taller, it is the V1 that changes the height, NOT the A1 track.

I tried the height changing operation in Shotcut 19.10.20 ( appimage version and flatpak version ), the result is the same.

I don’t know If I made a wrong operation.

My OS:
Debian Stretch 9.11
Gnome 3.22.2

It works for me, but they increase at different rates.

You are right, I can indeed increase the height of the track.
It’s just that the height increase of the two tracks is not the same, so I mistakenly think that the A1 track does not increase the height.

Thank you~