Help! New FD 50mm f/1.4 silver mount release button not coming out and locking when mounted

I have an AE-1 Program and recently purchased a Canon 50mm f/1.4 FDn on Ebay, however when I received the lens it doesn't seem to be snapping and locking into place when I fully twist it onto my camera (which works for all of my other FD lenses). The lens rotates to its full mounted position, yet the lens' mount release button will not come out to lock the lens in place so I'm able to rotate it back off the camera. I made a short video demonstrating the problem, and comparing it to my 28mm lens which properly locks (this was for the seller), and a second video to show the back side.

 

Video of the problem (50mm compared with 28mm):

 

Second video of the back of the lens (50mm):

Pictures here: 50mm 1.4 lens mount won't connect

 

I can't find any solutions for this anywhere and every part of the lens looks to be in proper shape to my eyes, except that the silver button doesn't pop out and lock when mounted. Any idea what the problem could be or how this could be remedied? Any help would be much appreciated!

So gordon ---

 

I just tried one of my FDn lenses to compare against your lens video. At full clockwise rotation of the lens unit (as yours appears to do in your lens video), the button should pop out and lock with a distinct CLICK. The fact that yours does not would indicate to me that perhaps a spring or such at the lock button area is defective. Perhaps someone who is more familiar with the lens construction will pop in with more info.

Bueller? . . .

Bueller? . . .

Ferris Bueller? . . .

Another reason why I'm not a fan of FDn lenses. I, too, have an old FDn 28mm that does the same thing. I figure some dirt has gotten inside the mounting mechanism. I don't worry about it. There lens stops down as it should and it's not really in danger of falling off.