I'm using Premiere CS6 and have currently no issues, everything works fine again with the new software.
The problem that you might have (Novasteve 74) is most likely that you have not having a proper sequence Preset.
Premiere CS5/6 is not directly prepared to work with 4 K Videos.
You have to generate your own Sequence Preset and also when later exporting the video a set of 4K Export Settings.
When you search in the Adobe Premiere Forum for 4K video on CS5 or 6 you will find some good instructions.
