I'm running Linux Mint 17.3 Rosa, Cinnamon. Functionally, RadioTray does work, but if I try to open a group, it only shows the top station, The same problem applies to any collapsible item such as "Preferences". Also if I am playing any station, the tray dialogue box now exceeds the size of the screen, and I am unable to change station or even stop streaming. The only way to do that is to quit the program entirely, or I have noticed that if I highlight a selection with the cursor, I can navigate to the unseen selections with the cursor keys, but I'm navigating blind there.
I'm not sure if you'd call this a bug, maybe it only affects people who use themes that use collapsible menus. I can scroll through the group, but only at less than one item at a time and not while anything is playing. If the dialogue box itself was scrollable or tweaked to more efficiently use space, that would solve its vertical height problem.