Taken from the thread
http://www.project1999.org/forums/sh...?t=6098&page=4 and was posted originally by mitic-
Insta-Clickies (and them only) are able to be clicked while singing. I believe this is why they started adding .1 cast times to "insta-clicks" but things like insta-invis and manastone we're able to be clicked while singing (and still are.)
*I know this is hardly related, but it is correct that bards can cast items and move without being interrupted (like Pegasus cloak.)*