Hi all,
We have setup Stash the same way the Stash dev team does (hopefullly), by following this blog http://blogs.atlassian.com/2013/10/inside-atlassian-feature-branching-on-the-stash-team/.
A quick sumary about the setup for those who do not have time to read the blog:
Its essentially a feature branch model, simailr to the gitflow model but without the long lasting 'develop' branch -- master is the develop branch.
We use the default naming convention suggested by Stash:

Now, here comes the question: we enabled the automatic merging, hope our bug fixes that go against stable-9.9.0 will fly into stable-10.0.0 as well as master (11.0.0).
The automatic merge got triggered as expected, the PR against 9.9.0 went in, however the automatic merge to 10.0.0 failed due to conflicts.
If looking into the details of the conflict, beside the files changed as part of the fix, it lists every single difference between the 9.9.0 release branch and the 10.0.0 branch.
Those changes including the pom.xmls for maven -- 9.9.0 has version number 9.9.0 whereas 10.0.0 has 10.0.0 defined in the pom.
This pretty much means, there is no way the automatic merge will ever work due to those conflicts.
So, what have I missed? What are the usecases Stash have in mind for this auto merge feature
Was this caused by the PR against a older release branch was created off that branch?
As the PR actually contains the entire branch, not only the changeset, hence the auto-merge fails due to there are indeed changes. If the merge, behaves like cherry-pick, or the PR contains just the patch not the entire branch, this should work.
Oh, btw, we are still on stash v2.10.1. But will update to 3 very soon.
Thanks in adance.
Jason