Eclipse Photon appears to be re-rendering the screen on every keystroke and mouse click. This results in a jumpy motion that sees the menu being hidden and the menu bar partly draw.
I have attached an image that shows the effect after the refresh. You can see here that the text menu is not visible and the menu bar is partly shown.
UPDATE:
I have narrowed this behaviour to the constant redraw of the bottom statusbar, as can be seen in the second image.
I have added an additional image that shows the effect when the window is not full screen.