Google-forms – How to setup form for multiple answers for one question

I want my google docs form to allow up to three days to be chosen by our users for lab reservations. I've tried allowing them to enter text, but they make errors. I have tried putting 1-31 as list items for them to choose multiple days, but it randomly generates false dates such as 7/28/2037, rather than list the 3 days chosen, occasionally. It lists the correct dates chosen most of the time. I need it to list the dates chosen always.