1. Window > Reset Windows (just for sanity)

2. Drag the Files window from the default docked single Netbeans window, off to the secondary display.

3. Click on the editor (on the primary display).

4. Click on the floating Files window.

5. Upon focus, the Files window jumps to a position on the primary display.


Same goes for any other windows floating on the secondary display: Search Results, Projects, etc.  

Anything that activates or gives focus to a floating window will cause it to jump to the primary display.  For example, if I drag a Netbeans floating window on top of an existing Netbeans floating window, the window underneath will reposition itself upon the "drop" event.  

Or if I use Command-Tab to switch to another app (e.g. my email), then Command-Tab back to Netbeans, one of the floating windows will jump to the primary display.  If I repeat that, all floating windows will eventually reposition to the primary display, one by one.

I've tried various permutations of options within Options > Windows... No difference.