On recent universal version on Ubuntu 16.4.1, the Delogo filter preview window is oversize so that the two lower buttons are almost entirely concealed.
As a workaround, depending on window manager and desktop environment, you can grab an oversized window at any spot and drag it beyond the upper edge of the screen when holding the Super (GNOME) or the Alt (all the others) key to reach otherwise hidden GUI elements. I do hope that at some later time the entire video zooming / GUI resizing logic will be redesigned, fixing issues like this one.
By the way, the real bug is that if the video in the preview of the delogo plugin is somewhat zoomed out (which happens if the video is as large as the screen or larger), the position (x,y) of the box which should be placed where the logo is, doesn't match the position of the mouse. It looks like the whole GUI is downscaled while the mouse position is not.