How to replicate:

1. Type message into commit window in the File Status tab.
2. Click on another program or window (either directly or using the taskbar)
3. Click on Sourcetree again.

When Sourcetree regains focus, it will refresh and erase the commit message. This happens every time, it is not intermittent.

If the user clicks on another tab (such as Log/History) after typing a commit message, Sourcetree will at this point store the message and prevent it from getting erased. Any further modifications to the message have to be protected the same way (by clicking a tab), or else the message will revert back to the state it was in the last time it was "saved" in this fashion.

It's ironic that I'm forced to write my commit messages in another app in order to prevent my source control software from deleting them.