When I press the Windows key or click the "Start" button in the DF multi-monitor taskbar to open the Start menu in my secondary display, it correctly shows up in that secondary display.
BUT if once opened I start typing anything to search for a program it jumps back to the primary display... this has been like this for forever, and it's not how it should work.

Ahm, ok. I hope you get to solve this at some point, because it's very frustrating.