The trouble is that height of control jumps, depending on actions, which you do, so I cannot write stable tests, which could check the borders of control. And control sometimes drops font.

If you remove custom font setting via css, everything will work fine.

Well, run the attached project twice. We will do 2 scenarios :

Scenario 1 :

Focus is on button initially.
output : New height 20.798828125
Click the button :
output : New height 19.1533203125
Move focus on the control (via mouse):
output : New height 17.9533203125.

Scenarion 2 :

Move focus on control (click in it)
output : New height 20.798828125
Click Button
output : New height 19.1533203125
Click control again:
output : New height 20.798828125
also, at this moment font was dropped to the font, which is set in the css.