It behaves like there are uninitialized, incorrectly initialized, or corrupt (e.g., memory overwritten, as by a stray pointer) values being captured for the display size. The bug is sensitive to the orientation of the iDevice when first launched, and to the starting state of the app. The problem will recur when relaunching the swapped out app, but doesn't alway recur when relaunching a check pointed app or deleted and re-installed app.
The bug typically looks like controls to the right of the portrait mode width being nonfunctional when in landscape mode, or controls below the landscape mode height not working when in portrait mode. Flipping the iDevice 180 degrees moves the unresponsive area to the opposite end of the app and allows one to use the formerly nonfunctional controls.
Retired Apple Display Software Weenie