Hey raf!
I expect you're already working on implementing the new features from the Mac version in the iOS app. Just yesterday I experienced a strange display bug I'd like to share with you. It happened when I connected to a VNC server (over VPN), disconnected and connected to a different one. When connecting I experienced that only a portion of the screen was used, even when changing the zoom level or going to fullscreen. When disconnecting I experienced even worse display bugs and when connecting again to the same or other VNC servers it even got worse. The only solution to end this was manually closing the app (double tap home button and remove from background apps list)
Sadly I wasn't able to reproduce the problem, but maybe it has something to do with the different screen resolutions of the two PCs I connected to. The first (that worked well) had a standard FullHD resolution. The second one had a resolution with a 4:3 aspect ratio.
All machines I connected to were Windows 7 PCs running TightVNC v2.5.2. My iPhone 3GS is running iOS 5.1.1
Best regards,
alexschomb