Addon settings windows not working

[DeleteFromUsers]

I'm using Leia 18.2 and when I open the addon settings window (using the right-click contextual menu), for configuring a video or a program addon does not appear any setting. It only shows an empty windows with the options cancel and defaults. This behaviour happens with every addon I've checked. I attach an screenshot showing the error:

Thanks for your effort. Its a quite nice skin.