Canon AT-1 mirror and shutter malfunction

[Th0rz669]

Hello. I am a student at a local college, currently taking a beginning photography class.

I have a Canon AT-1 camera, and it was working fine for the last few weeks. Until today..
I was out in the forest taking some picture. I had taken about 5-7. Then I turned the lever to advance the film, and then suddenly, once it has advanced all the way, the camera fired..

I tried it a few more times, and it kept firing. So I went into the photo lab, and opened it up in the room where we load the film into the developing canisters. I rolled the film back into the canister, and placed it into my bag. So I tried the lever again, and the camera fired! So this time, I left the room, and I opened up the back and took off the lens, and tried the lever. The shutter was not opening, but the mirror was going up, making it impossible to press the button to open the shutter. Every damn time I pulled the lever, the mirror would go up. Unless I held down the button, in which case it would raise the mirror and open the shutter normally, but only when I turned the lever.

I brought the camera to my teacher, and he has no idea what's wrong with it. Has anyone here had this issue with this camera (or a similar camera) before?