I went to Menards tonight after we filled the tank with gas, so that I could get a fill on LP. The girl screwed the nozzle on the fill port and pulled the trigger, gas shot out the vent, so she tried ...
Being that it's bone dry, it could indicate a leaky pressure relief valve. Ours never is allowed to go below 1/2. Always stored for the winter full. There is a chance you have contamination (rust) that caused the valve to stay open after she cracked it a bit.
I suggest having a professional look at it, and tell them it was dry for a year.