Zoom not staying put in Manual.
 

Just messing around with one of our EX1s today and I noticed something interesting. With the lens pointed straight up and the zoom in manual it will not stay at full wide. The weight of they glass pushes the ring back about 10deg. I don't know if it's just that one camera or all of them. There's very little friction on the zoom ring so it's easy enough to see how this is happening.
Probably not a big issue, I'd very rarely be pointing a camera straight up anyway.

So that's what that was. I noticed the exact same thing once but it didn't happen again so i just forgot it, now come to think of it that one time it was pointed upward.

Good to know! I was wondering about why the zoom setting often changed. I have the LEX so I normally keep it at z80 so its easy to notice if it changes. It usually goes in or out by 1 or 2. I shoot at sky and trees often. A quick test and it seems to happen less if you're in manual mode.

It's a very annoying thing when it happens mid shot. Certain Panavision Primo zooms do that too. I usually just engage the motor and that adds enough resistance.

-Sean

I had this problem with the camera set on a car.
I fist set the zoom to manual, but while the car was moving, the zoom ring moved.
Then I set the zoom as I wanted and switched to the "motor", to stop the zoom ring to be able to move.

The vibrations of the car also changed the zoom.

The solution is to gaffer it :)

Canon 'L' series stills lenses do the same thing... Weight of the glass.