I see this a lot, even though it says charge complete, the pin is still up holding the plug in place.
Im thinking maybe it's waiting for an 'Ok Im done too, its safe to unplug' or something from the charger as well before it disengages, for safety reasons? Not entirely sure on that.
You shouldn't really force it to let go, that's just asking for issues IMO. You force something, and it bends or breaks, now what?
Although it is a bit of a pain, just cycle power on the bike and it'll send a 'cycle' command to it to retract the locking mechanism so you can unplug properly.
Aaron