Using the Rich Text editor and ImprovedMediaPicker Package I noticed an issue with the save to.. dialog loads an iframe which has issues scrolling. This is due to the height on the iframe in /umbraco/dialogs/treePicker.aspx being set to 370px. As this is referenced by popups 200px in height an overflow occurs and some nodes are unselectable. Removing this height fixes the issue. This bug appears in at least 4.0.3, 4.0.4 and 4.1RC.