Macro for marking a thread as read and advance to the next unread message

[romildo@xxxxxxxxxxx]

Hello.

I have a macro defined in my mutt configuration
file that should mark the current thread as read
and jumps to the next unread message if there is
any, or stays in the current message if there is
none:

  macro index <F5> <read-thread><next-new-then-unread>

It works as described with prior versions of mutt,
but behaviours differently with mutt 1.5.6i. With
that version of mutt it marks the current thread
as read, and skips to a following new message.
The problem is that if the next new message is the
one immediatelly following the thread marked
as read, that message is skipped.

Has anybody seen this behaviour? Any comments?
How to obtain the old behaviour?

Regards.

Romildo