I updated to Ver. 3.1.6345 yesterday and I'm seeing a similar behaviour to @squigglez.
In 'Artist and Tracks' view, when I sort by 'Album Artist/ Album' the Various Artists albums end up being sorted incorrectly.
All albums tagged with Various Artists in the Album Artist tag appear in the middle of 'F' in the list.
For example:
The Focus Group - Elektrik Karousel
Various Artists - 12" 80's Classics
Various Artists - A Boy's Own Odyssey: Acid House Scrapes & Capers
Four Tet - Pause
When I looked in the sorting tab, all Various Artists albums had 'Forest Mighty Black' set as the Album Artist sort string.
When unticking "enable custom sort values for individual artists, composers and albums" in "Edit - Preferences - Sorting/Grouping" the list sorted correctly.
Ticking the 'enable custom sort values' again returned the original sort order and the same 'Forest Mighty Black' sort string.
This doesn't sound like it is intended behaviour to me.