The Berlin Project

Reproduction:
1. Start demo, multiline text demo
2. Put mouse cursor on the middle button (which shows
the position of the viewable area), hold primary mouse
button
3. Move (drag) the mouse to bottom until the button is
at the lower end.
4. Move (drag) mouse up top until the button is that
the inital, top position again.

Expected result:
At any time between step 2 and 4, the mouse cursor is
on top of the button.
I.e. to move the button 3 pixels down, you have to move
the mouse cursor 3 pixels down.

Actual result:
After step 3, the mouse cursor is way lower than the
button, if your berlin screen is large enough at all to
carry out step 3.
E.g. to move the button 3 pixel down, you have to move
the mouse cursor ~12 pixels down.
("Mouse cursor" here means both the little dot and the
arrow that is drawn.)
After step 4, the mouse cursor is on top of the button
again.