Sanity check: Am I using onHover correctly?

I've tried adding this code to both a marble and to a custom board:

function onHover(player_color) log("hover") end

Nothing gets added to the log when I hover over either object. This Global code, on the other hand, works perfectly:

function onObjectHover(player_color, hover_object) if(hover_object ~= nil and hover_object.guid == MARBLE_GUID) then log("hover") end end

Am I doing something wrong, or have I run into a bug with the onHover event?