When using a btn-group and using btn-rounded, the CSS styling works by looking at the first and last child, buttons in the middle don't get rounded corners.However, when putting a mdbTooltip on the buttons, the tooltip dynamically inserts a child at the end, causing the previously mentioned CSS style to break.

So what happens: onmouseover, the tooltip appears adding an HTML element next to the button in the btn-group, the CSS applying rounded corners to the last child of the btn-group breaks and the button becomes rectangular again. Oh and also the tooltip doesn't show for the last button in the btn-group.