Propane inspection "required" in IL?

Concerning portable tanks, I ran into something new to me a couple of weeks ago. I was at my local lumber company which also fills propane tanks. I had a 30 lb tank from my 5'er and two 20 lb tanks that I use for outdoor heaters at a friends patio where we sit out at night. I arrived at the fill station with all three tanks in the back of my pickup. After the first one was filled I put it back in the back of my truck on it's side which is how I have always transported them. Standing up they have to be tied in place which is a pain. The attendant stopped filling my second tank and said that I would have to transport any filled tank off of his premises standing up or he could not fill the other ones and would have to confiscate the one that was already full. He said one of their other fill locations was "caught" allowing filled tanks to be transported on their side. This location was fined $10,000.00 he said. He said portable tanks on their side disables the anti leak valve and thus is illegal to do. I looked on the label on my tanks and they do say to transport only in a vertical position.

Anyone else heard of this?