This whole thread seems to have gotten out of hand. The OP simply asked if anyone else had experienced this, she did not ask to have her parenting skills critiqued.
Sure, it is just a picture followed by an autograph. I can see how it seems like a trivial thing to get worked up over. But remember, there was a 2 year old. A 2 year old that was seeing Mickey for the 3rd day in a row. The 2 year old probably thinks it is the same Mickey, as well as the real Mickey. Mickey signs books first for 2 days, then hides them on the 3rd day. In the 2 year old's mind, Mickey is suddenly being mean.
Yes, we can make excuses for Mickey, but the bottom line is that those people in those suits are getting paid to make visitors happy. Also, visitors are paying hard earned money, and plenty of it to be happy in those parks. If you're in that Mouse suit, and a child starts to fuss because you took something of his, you give it back promptly.
For the OP, next time, you could suggest to Mickey that he sign first, since he did that yesterday at Epcot
but ultimately, Mickey needs to do his job to make the customer happy!