I've found a bug report of a similar issue affecting the SourceTree 1.9.1 too, as you can see on the following link:
It was reported on May/22/2014.
Could you please try to update the SourceTree to the latest version and let me know if it still happening?
Supported Platforms macOS Windows To make using Sourcetree as simple yet powerful as possible we embed (bundle) dependencies such as Git, Git LFS, and Mercurial. We strive to keep these...
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