I've managed to get the pin to function as both sink and source with out issue on the PLUS+1 Hardware.
Issues arises with the relays I am driving externally.
As the configuration is basically 2 relays in series, the coil holding voltage once energised is high enough that the relays do not energise.
24V system, 2 relays in series, sees 12v across each coil, this is enough for them to energised.
I believe I can you some kind of diode configuration but I haven't worked out which yet.