Steps:
1) Pressed Commit button to start a commit.
2) In the resulting commit dialog, I created a comment that began with: [WIN]
Once the commit finished, the GUI updated and showed the attached error message. At this point, the Log/History tab only showed 'Uncommitted changes'...the rest of the log wasn't there. Because of the log error, I figured the issue was with the all caps or the square brackets.
3) Clicked on Terminal button to bring up a terminal
4) Executed: git commit --amend -m "[Win] rest of message"
This resulted in the same error and Log/History view.
6) Executed: git commit --amend -m "Win: rest of message"
This fixed the issue. The Log/History was populated.