Comment 8 for bug 1543642

Yes, the panel obstructs maximized windows still.

Tested with:
- downloaded artful-desktop-amd64.iso (Ubuntu MATE 17.10)
- made bootable usb stick out of it
- booted laptop
- plugged in external screen (hdmi)
- configured display layout with external screen above laptop display and leaving laptop display primary with panels
- opened home folder from places and maximized the window
- result: top window bar (with the close, minimize, maximize icons) is hidden behind the top panel on the laptop display

If you need more details please point me at the right direction.