This bug makes the synthetic history generated by SourceTree incompatible with other subtree users. The root cause seems to be an extra "-n\n" in the commit messages generated by the embedded version of Git.

Steps to reproduce:

1. Clone this repository: https://bitbucket.org/jennings/sourcetree-subtree-commit-message-bug
2. Set SourceTree to use the embedded Git (version 1.8.4.2)
3. Use "Add/Link Subtree" to link the "sub" directory with a remote repository.
4. Push the subtree.
5. Set SourceTree to use the system version of Git (tested with version 1.8.5)
6. Push the subtree.

Results:

The subtree created using the embedded Git has a head commit ID of 6e92039. The subtree created using the system Git has a head commit ID of 329f350. Resultant repos can be seen here:

https://bitbucket.org/jennings/sourcetree-subtree-commit-message-bug-embedded
https://bitbucket.org/jennings/sourcetree-subtree-commit-message-bug-system

Expected result:

Both branch head commit IDs should be 329f350.