Found in Blender 2.57b on winXP, but not in 2.56a/2.57b on Ubuntu 10.04

Switch any window to UV/Image editor using Shift+F10 and all editors stop receiving input. Switching to any other editor type or using the dropdown menu to switch did not result in this problem.

This is especially apparent if you switch e.g. the properties editor to UV/Image editor: now you can't move the camera in the 3D viewport anymore (middle mouse button is ignored).
The problem wasn't there in r34644, r35161, r35349, but I found it in r35453, r35566, r35865, r36200, so it was introduced somewhere in between.

You have to right- or left-click somewhere or press any key so you can work in the editors again.