Heads from merged branches

[anatoly techtonik]

On Mon, Dec 2, 2013 at 1:07 AM, Christophe HENRY <listes at sbgodin.fr> wrote:
> Le Mon, 2 Dec 2013 00:51:39 +0300
> anatoly techtonik <techtonik at gmail.com> a écrit :
>
>> I am using Mercurial 2.6.3 on Ubuntu. Why it keeps showing me commit
>> from inactive merged branch in heads? Is it really necessary, or a
>> bug?
>
> You want to view topological heads, that is heads without children.
> For this, type in: hg head --topo
>
> More info with: hg help head

This is confusing.
If you need to know about active branches, you use branches command.
I can understand heads that were not merged back, but why heads shows
branches that were merged? Is it really necessary to have this default
behaviour?
--
anatoly t.