Reproduction steps

1. Create a panel
2. Use it at a tab panel:
   
3. Use this tab at your dashboard
4. No go to the panel (in this case W545)
5. And try to take a look if you can see that this panel is used at your dashboard:
   

The problem: normaly you can use this information, to check if other people are using this panel, then you may hesitate, if you want to edit the board.

Version information

I'm feeling like you, I get 403 too...., sorry. (See here) (if absolutely needed, I can ask an admin at Wikimedia later, and add this information)