F5 Trunk port is connected to Cisco Switch Access Port

It shouldn't do, because as said earlier 2 interfaces in a port-channel will never bridge. But I wouldn't enable port fast on a link to a BigIP. Portfast should ONLY ever be used when connecting to SERVERS that are incapable of bridging (i.e. Only have 1 interface is a good start :) )

NEVER connect a port fast interface to a switch device (And the BigIP should be considered a switch device as it will quite happily bridge interfaces if you tell it to).

H