I get UI freezes with the last Update.... (I also got one system freeze 2 days ago)
I used to have this issue before and in my case the only way to solve the problem was to burn the firmware again but first starting with a brand new download, extracting the image file and saving it to the DX50 internal memory. Then I would perform the update, wait until it starts up and finish with the factory reset. If I follow those steps closely I just do not get any freezes.
Hope you can solve your problem.