What I just did to test was open designer at about half size of my monitor. I added a viewport with fit layout. I added a panel to the viewport. Make sure the film for the newly added My Panel is focused. Resize Designer. The film for the viewport resizes accurately. The film for My Panel resizes, but not correctly.
If there is a better way to demonstrate what I'm seeing let me know. If there is a good screen / video capture method I can use that if you want once I'm home and not on my corporate machine.