Warning: technical explanation ahead. If you consider it illogical or plain stupid, you have to take my word for it. :)
With mouse based head rotation vorpX has to apply head tracking while in EdgePeek mode to ensure the game camera is still rotated correctly after leaving EdgePeek. Theoretically it should be possible to just ‘record’ head movement and then apply the difference from before EdgePeek later, but that never worked reliably enough to be ready for prime time. Might come some day, but the list of nice-to-have-stuff is long, so no promises.