Sounds like the float is stuck.
I had this happen with a 100lber (no OPD over 40lbs), idiot at the station didn't bother to check and stuffed 25 gallons in, even though the tank wasn't empty.
Missus called me at work when the weather started warming up some time later, and the tank started venting. I raced home, unhooked the tank and got it onto a hand truck and out into an open field.
As I went to open the bleed valve to vent it, the safety vent fully opened and nearly knocked the tank over (Nothing like a 3/4" opening venting at near 300 psi to make you need to change your drawers).
After that happened the tank stop bubbling, but I still bled it for an extended time via the bleed screw just to be safe.
Don't take them in with anything left in them anymore, on the off chance I get another idjit at the station.
