I'm running Avidemux 2.6.7 in Debian linux, in the Preferences dialog there are a couple of check boxes that seem like they shouldn't be there. In the Display tab there is a check box with no label and in the HW accel tab there is a check box next to "If you use Hw decoding, it is better to use the matching display driver", which shouldn't be there since it's a warning.
Also, when I open Avidemux there is a white rectangle next to the sidebar.