Mercurial: Unable to push to remote repository after pull-merge-commit

I can't figure out why i'm still unable to push to a remote repository:

>开发者_开发技巧; hg pull
pulling from ......
searching for changes
no changes found

> hg merge
abort: branch 'default' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads)

> hg heads
changeset:   12942:...
tag:         tip
parent:      12940:...
parent:      12941:...
summary:     merge

> hg branches
default                    12942:...

> hg commit
nothing changed

and finally

> hg push
pushing to ...
searching for changes
abort: push creates new remote heads on branch 'default'!
(did you forget to merge? use push -f to force)

why would that be?

---

Not sure why, but this solved the issue:

hg push -r tip

where -r is

-r --rev REV [+] a changeset intended to be included in the destination