had the same issue with a new tvseries button, for me they worked after changing the names to:
button_mp-tv series.png
buttonNF_mp-tv series.png
hover_mp-tv series.png
hope this helps!
..., but for some reason hover_mp-tv series.png is not used and the regular custom icon remains displayed.
As I also tried to use the same for the my movies plugin and strangely enough, it is working there the other way around. I used the plugin.dll name for convention, but
button_MesFilms.png and buttonNF_mesfilms.png do not work, but hover_MesFilms.png works properly.
Any suggestions for help?
thanks,
Patrick