Why is "Paste, on the fly" a no go?

Grabbing a region I wanted to "pop it in" at several places, it was a guitar riff, and there is no math or set patterns to my arrangement decisions, I put things here, there, everywhere, like anyone.
While rolling I pressed the Apple V command to paste the riff "on beat", it wound up way back from where the cursor was (which was a bore) & when I pressed Apple V again nothing happened!No further pastes possible. What is this? Do one paste then stop functioning?
How can I "pop things in" on the fly intuitively with no grids, markers etc? Obviously a sampler could do it but PT has got to be better that that , aint it?
I RTFM, I must have missed it. How is this most basic task done by you guys out there? I am sure I have seen my chums running Logic Audio do it, what about Pro Tools?

Thanks



Jules