Weird problem, the shutter curtain goes up after advancing the lever.

Weird problem, the shutter curtain goes up after advancing the lever.

When I advance the lever the shutter curtain goes up by it self without releasing the shutter, the weird thing is that the shutter still fires and the curtain comes down after that certain time. This does not happen every time but after a few advances it goes up and stays there until I release the shutter. I checked the magnets all seem to work fine and also the battery level is normal.