Transparancy slider for logo is reversed
Go to Adjustments and Effects dialog (Tools > Effects and Filters). Go to Video Effects > Overlay tab.
It says: "Transparency" "none" "full"
But when the slider is set to "none" the image is transparent, and when set to "full" it is not transparent.
So maybe reverse the values of the slider, that way 100% transparency is when the slider is all the way to the right.
Maybe even remove "none" and "full", it seems none of the other sliders in the dialog tells the user which side gives a higher value.
Tested on Windows 7 in VLC 2.2.1 stable and vlc-3.0.0-git-20150802-0403.