Description of Problem:
In a thread view you may collapse certain threads to save vertical space
and read other messages.  Once a thread is collapsed new message may arrive
inside the collapsed thread hierarchy.  Choosing 'Next Unread Message' does
not take you to the root message of a thread hierarchy, instead it does
nothing however Evolution still indicates that you have new messagees and
it's now your job to find them.

Steps to reproduce the problem:
1. Collapse a thread in the thread view with unread messages in the thread
2. Mark all other messages outside the collapsed thread as read
3. Use 'Next Unread Message' trying to find the unread messages in the thread

Actual Results:
The focus does not change

Expected Results:
The focus should move to the root message of the collapsed thread

How often does this happen? 
Every time