Broken: 2.70 f93bc76
Short description of error
If multiple windows are open (but same Blender instance), shift+click or ctrl+click on the unfocused one (to pan or zoom in a viewport for instance) will be taken as a simple click instead. It makes working with floating viewports difficult since one must focus the window first, then act.
Exact steps for others to reproduce the error
Pop out a new 3D view by shift-clicking the corner, switch from one to the other using click with any modifier key (ctrl or shift).