Comment 3 for bug 500663

This is actually part of the specification but hasnt been implemented yet > wiki states
"if a notification bubble has been fully visible for 2000 ms when the pointer enters, it should switch to its mouseover appearance until the pointer leaves, then switch back to its normal appearance and display for a further 3000 ms. "
https://wiki.ubuntu.com/NotifyOSD#Animations%20and%20durations