Reusable mug refused by Starbucks

Last weekend, my boyfriend and I headed out to Lancaster County, to attend the wedding of some friends. It's about an hour and a half drive from Philadelphia, and when we were about halfway there, we stopped to use the bathroom and so that I could get a cup of much-needed coffee (in our hurry to leave that morning, I had neglected to make myself any).
One of the green choices I make on a daily basis is to always tuck a reusable coffee mug into my bag, so that I can indulge my caffeine habit without consuming throwaway cups. So when I walked up to the Starbucks counter at this particular service plaza, I had my reusable mug ready to hand over as I placed my order of a tall coffee.
The woman working the counter held her hands up as I tried to present my mug and said, "We aren't allowed to accept reusable cups. It's against health code." I was flabbergasted, as I had never in my life had my reusable cup refused (and I've been using them since 1993). Before I could turn away and cancel my order, they had a regular paper cup sitting on the counter. I didn't want it to go to waste (and sadly, I really wanted that coffee) so I paid for it and took it, feeling both a little dirty and outraged at the same time.
For those of you out there who are travel mug devotees, have you ever had your cup refused? Are there many other areas of the country that believe them to be a health code violation?
Last Sunday was the opening day of my favorite Farmers' Market in Philadelphia, the 















