When I switch between my IMAP mailboxes it sometimes fails to scroll the
message list to the right possition. The last mail I read is selected and
shown, but it is not sure it is visible in the message list.
And when I start evolution it hasn't happened yet that it has scrolled down
to the message I last read.

I have tested this only on IMAP, since I don't have any local mailboxes.
What I did to test this was first to go to my last message in my mailbox
(not INBOX, don't know if it makes any different but anyway...), select
that so it is shown. Then I exited evolution from the menu.
I then started evolution, after it has retrieved the mailbox list it
doesn't  select the mailbox I last read (this is not a big problem but I
still assumed it should to that). Then when I manually selected that
mailbox I'm possitioned at the top of the message list (not at the bottom
as I expected). However, the selected message that is show is the one at
the bottom of the list (just to be clear, I doen't see the selection but
have to use the scroll list to find it). 
If I then select another mailbox and then switch back to the first one I
might be possitioned at the correct place some times and sometimes not. 
This is quite random, and I doen't alway get possitioned at the top
sometimes I get possitioned some random place in the message list.

Summary: 
The message list possitioning code is not very reliable on IMAP mailboxes,
it might have something to do with the network but that is just pure
speculation.