MySQL active connection never bleed off to other pool member

Were you expecting the BigIP to automatically connect an existing TCP connection to another host without the client having to participate?

Even for the most basic of protocols (e.g. DNS, SNMP), this won't happen. When the pool member goes down you will (by default) device a RST to indicate that connection is no longer valid. You have the option to send the mid-stream connection to another host, but as that host has no idea of the connection, you will (again) recieve a RST. Now you can (In theory) write an iRule to migrate MySQL connections from one host to another (Triggered when the pool member goes down - this is where you'd normally recieve a RST back to the client). I have done it in the dim dark past for LDAP, but in practice it isn't trivial (And possibly non-practical, but I'd love to see someone do it) You'd have to implement a protocol specific proxy to track what was sent and what was received. For a SQL database you'd have to track transactions and be ready to replay the whole transaction to the second server if you had to migrate it for any reason...

Given it's usually a pretty application specific thing I'd probably suggest altering the app rather than the BigIP to accomplish migrations of MySQL connections). Or running mySQL Cluster which does (apparently) guarantee uninterrupted access from clients... but I've never tried it and I'd suspect it's not cheap either...