A user with partial permissions to a list gets Access Denied when expanding ListView grouping.

This is a bizarre bug.

The setup

• Take your basic SharePoint list, a few levels of grouping and lookups.
• List items are separated in folders in this case, which then are security trimmed to groups
• Not every member can see list items in each set
• When you expand the ListView webpart, you get an Access Denied error.

A quick fix

Thinking this is something to do with Postback, I ticked this option:

Life's good again.  No idea why.  

Speculate away!  Let me know in the comments if this helps you in the future.

:-)