Is it common to lose a part you were given?

I feel I have to tell someone about this. I've worked my tail off on several local productions as a production assistant. I didn't learn as much over the years as I'd hoped and wasn't moving up the ladder at all. I live in a small city and all film professionals know each other. They really didn't see me as anything but a P.A. I decided to try my hand in front of the camera. One of the many reasons I quit training for theatre was a fear of auditioning. Because we all know each other, I was easily hired for a local commercial by a girl "Kris," I've worked with on another project. That went smoothly and she encouraged me to audition for a film she was working on. I got my first head shot, my first little humble acting resume and did my first audition! I was so proud of myself for facing it. I felt I did well. The director and camera chick started nodding, like they were getting into it. When I was through, the director said I was "definitely in." I waited for my instructions. Weeks went by and it was getting closer for the first production day. I saw the director and "Kris" at a bar. He seemed uncomfortable. I told Kris I'd like to know what part I got. She actually took a step back and referred me to the director. Uh oh. I just couldn't ask him in a bar. I waited another week and sent him an email. I reminded him that I was told I had a part, said I'd been waiting, that I felt it was inappropriate to ask him about it in a bar, that I think it's inappropriate that I contact him now, but if he'd changed his mind, I'd like to know. Kris contacted me shortly and apologized for not following up with me, told me I didn't have a speaking part, but could come by set that night to be an extra. I decided to be positive and told her I'd love to. On set, neither she or the director seemed apologetic for giving then taking away my opportunity, although he thanked me multiple times for coming. Both were a bit rude to my surprise. I was partnered with this sweet girl for the night. We mimed conversation in the background. When the assistant director spoke to us, she refused to look at me and would only address the girl. I worked for a sandwich and chips from 11 P.M. to about 5 A.M. and withheld my feelings until I was released so that I wouldn't make a goof of myself. I felt they were rude to me AFTER being rude to me! What logic is that? Now, I've worked (inconsistently) for years on small budget local productions. Am I being whiny? Am I supposed to suck it up and just be thankful I was allowed on set? If I hadn't contacted them, I wouldn't have had that chance AFTER being told I was in. I can't really discuss this with anyone in the know. When I was a slighted as a child, I'd vow to become more successful than those who slighted me and I feel the same way now. LOL My feelings are hurt.