Thanks, it confirms my initial thoughts.
The bug will occur whenever the video is loaded in a container window that is smaller than the image size.
Double clicking will ask the video to try to fill the screen, and this will correct the scale factor of the image, fixing the bug.
Coordinates of the drawings are adjusted with the scale factor of the image, this is why they jumps when it is corrected.
I'll make sure a fix is shiped in the next release.
(For a quick workaround, you can double click the image before you start to draw)


