800/5.6 tripod collar rotation problem

I just picked up a used Canon 800/5.6 in like new condition. The only thing that I can't figure out is that the tripod collar and mount only rotate a total of 90 degrees even with the lock screw fully loosened. When I mount the lens on a normal tripod in the landscape orientation, I am able to rotate the lens only 45 degrees clockwise or counterclockwise, in other words I can not move it into portrait orientation. I have to flip over the ballhead instead to get it into portait position. And when I mount it on my wimberly sidekick I can get it into portrait orientation and then 45 degrees CW or CCW, but then I can't get it into landscape position. The end points are rock solid, no chance that they can be forced.

What am I doing wrong
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Michael Gehrisch
http://www.pbase.com/kingfisher