I can confirm, that it opens correctly with the portable version, although I've a lot of personalized settings in the windows store one and there's an error when importing the settings snapshot so I can't check 1:1.
What I have managed to do is to save a settings snapshot, change "FormTagEditorDock" from "5" to "1" in the INI file (guess work - have not tried other values, 1 seems to work fine), reimport and now my tag editor shows up at the bottom of main library panel. If I revert it to "floating window" it no longer works.
With that workaround I'll happily wait for the windows store version update down the line as re-configuring all the settings is too much of a pain if snapshot import won't cooperate.