Thanks for the video, it should open on the screen it was last used on. Can do you me a favor and look at the minion.xml and inside there should be a line like this but with different numbers...
<position height="823.0" width="1285.0" x="189.0" y="233.0"/>
Move Minion to your other screen, and open the minion.xml again (or fresh the the doc if its open) and see if the numbers have changed?