DF titlebar buttons are overlapped by the buttons created by Teamviewer. This only occurs while Teamviewer is running. When Teamviewer is shutdown, the DF buttons reappear.
TeamViewer has an option to disable their buttons, or move them if you want to keep them. In TeamViewer, go to Extras > Options > Advanced, and click the "Configure" button next to the "QuickConnect button" label in the "Advanced settings for Computers and Contacts" section.
From there you can either disable it, or use the slider to move it left or right
