Right click on a tab closes the current editor, not the one clicked on.
(http://img9.imageshack.us/img9/2782/shot0014uv.png)
Notice above, that I've right clicked on the left tab, but it's about to close the right tab.
MSW XP sp2, SVN 5751
Should be fixed in svn r5827, by selecting the tab that sends the event before creating the context-menu.
The behaviour is now as it was before wxAuiNotebook introduction.
Wow! thanks.