If you position the panel on the right screen edge and select auto-hide from panel settings, the panel doesn't hide. But, if you put the panel on the bottom screen edge, select auto hide, THEN move it to the right edge, it hides properly. Also, the issue re-appears after a restart - if you leave the panel on the right screen edge (whether it's auto-hiding properly or not) and restart, once you log back in, the panel will remain visible on the right screen edge and won't hide until you go through the same process of moving the panel to the bottom screen edge, enable auto-hide while it's there, then move it back to the right screen edge.

Reproducible: Always

Steps to Reproduce:
1. Move panel to the right screen edge while it's still always visible
2. Enable auto-hide while it's docked on the right screen edge
3. Gasp in horror as it remains visible

Actual Results:  
The panel remained visible

Expected Results:  
The panel should have hidden itself

I'm not sure if this is relevant (probably not, but I kinda just want something to put here), but my system uses the proprietary Nvidia display driver (version 343.22. The card is a GTX 760)