BAD GAS !

Yes, it's the ethanol causing the fuel to evaporate more quickly and turn bad more quickly.

I'm fortunate that in my neck of the woods most premium fuel has no ethanol, so if the car is going to be sitting for a while I'll use the high test with stabilizer and I'm good for at least 12 months. For the same reason I also use premium with stabilizer when filling up the jerry cans.