Disappearing change on pull rebase

Hi all,
I've got an issue with some operations. It seems like git eats one of my commits (it's still in reflog, but in normal tree, it's unavailable).

What I did is:

checkout -b feature/....
(edit files and commit)
checkout master
merge --no-ff --no-commit feature/...
(edit some files, change versions, changelog)
commit

Now I've got the change committed in the branch and some more changes on the merge commit.
So before pushing to the main repo, I'd like to check if any other changes are there:

pull --rebase

Now my merge commit disappears completely along with the changes without any warning. I get the branch commits duplicated on top of master and the branch stays as it was.
That looks like a data loss bug to me since I can only recover a committed change from reflog and there are no warnings before that change goes away (using 1.7.4.1). Actually no changes were done in upstream in the meantime, so the rebase was not even needed.

Regards,
Stanisław Pitucha
Cloud Services 
Hewlett Packard