I happened to me on August 15th in front of the Living Seas in Epcot.
I left my stroller out in the stroller parking and went in for the Nemo ride and Turtle Talk With Crush. We came out and it was gone. It was a Maclaren Stroller. It had some things in it, so my advice to anyone is if you have things in your stroller you would be heartbroken without take it with you on rides and in shows. We lost about $50 in souvenirs and had to buy another stroller while we were there. I will say Guest Services was not very helpful to us. They did replace our ponchos for free because they were in the stroller and it was raining that day. But in hindsight now it was only a stroller and it was replaceable. I just can't understand people sometimes...