Text on main nav bar buttons disappears randomly while SourceTree is open.

At various times during the day while SourceTree is open some of the text will disappear on the buttons at the top of the app. Generally when this happens it is all of the buttons from fetch to the right. I have attached a screenshot of the issue. Restarting the application will usually fix it, but after a period of time I will go back to the app and the button titles will be gone again.