Your playback may be set a half resolution, but returns to full resolution when you pause. Depends on how you have Premiere Pro set up for playback, and whether or not your system will support full resolution playback of your media.
Dell Precision T7600 (x2)
Win 7 64-bit
Adobe CC 2015.02 (as of 6/2016)
256GB SSD system drive
4 internal media drives RAID 5
Typically cutting short form from HD MP4 and P2 MXF.