Panel tray icon behaving unexpectedly (icon size animations)

[kode54]

The icons grow or shrink depending on mouse-over, and if I right click an icon that opens a menu, in this case, Steam, it will shrink again when I move the mouse off it. However, if I left click the Steam icon, it stays larger when the menu opens, and I have to mouse-over and mouse-out to shrink it again.