laurim
Hello,
Looks like it may be a setting issue. We have come across this where the source is outputting a specific resolution and frame rate and if it is not exactly matched on the Media Express side of things, you may see what you are experiencing.
For example, if your HV30 is set to output at 1080i 59.94/60 and you have Media Express set to 1080p 30, you will see this split screen. Setting Media Express to 1080i 59.94 in this case should resolve this issue.
Please check this and if you have any other questions, do let us know.