Four times now, trying to replicate it can't replicate it exactly, when exiting a raft I've had swimming automatically toggle 'on', and by toggle on I mean that I am able to swim.
When I click to toggle swimming after it does indeed toggle 'off', but now the picture shows (indicating it's toggled on but it is NOT).
I've been able to replicate it several times so far, with friends watching me in hopes that I die and they can steal my stuff (if only it didn't end up on the bottom of the sea), and I'm sure it's related to rafts directly.
I also found out you can throw rafts, funny little thing you added there, very fun : ^)