Dakotablue

Hi all, so I connected an extend stay to my propane tank and have a
Propane tank connected. But now I have to disconnect portable tank to refill.
My problem is that when I disconnect line from portable tank, there
is propane coming out of hose. I have the tank that is mounted on rv turned off.
Is the propane that is coming out the propane that is in the lines??
And how do I prevent gas from coming out? I have a 2014 sunseeker 3170.
Thanks for any help