Not that I've seen but not unheard of with some platforms to ensure no overdue monies are owed on purchases. Basically that says the broker doesn't have a good credit facility and I would have thought Commsec through CBA did. Could depend on if you bank with CBA too so have it all linked.
There's no reason, with tech these days, it couldn't go to T+1.
In any case, I doubt that has any impact on the ASX' current T+2 rule and the registries.