I do have to say this for what it's worth!! I was at a convention this past weekend and got a cup of regular coffee and a small amount of cream. I was drinking out of one of those paper cups (not sure of the manufacturer) but I got very sick for two days. I packed my own lunch, all gluten-free....the only thing I could think of was the coffee - which would be strange - OR THE CUP. So I don't know.... but for what it's worth. And who knows where they bought it from - it was a cheap paper cup.
Also - I saw that someone posted decaf coffee can have gluten in it through processing or something. I know they never responded but I have to say that about a month or so ago, I went to Dunkin Donuts (always drink their coffee and love it) and ordered a regular iced coffee with cream. Well I got it and it tasted really weird to me. Also didn't give me my "pickup" and it upset my stomach right away. I figured out they gave me decaf by mistake and it did infact make me sick. I thought that was weird - wasn't sure why decaf would make me sick but it did.