I have always used my HP35S in it carrying case. I have experienced keyboard problems particularly with the R/S key. But, today I belatedly noticed that the carrying case doesn't provide a very solid base. I took it out of the carrying case. Surprise! Surprise! The calculator is much more stable and I am experiencing far fewer keyboard problems.
The theory would be to have the force of your fingertip focused on the contact dome, instead of wasting it deforming the bottom of the elastic case, right?
Whats worser than a key with no tactile feedback? Right, a key with an unreliable tactile feedback. My only calculator showing this was a TI-59 unused for quite some time. After carefully cleaning it and replacing the foam, the problem went away. Hopefully, the 35s' problem is solveable as easy as that.
The 35s could be such a great calculator. It's a pity for all those bugs...
Edited: 17 Apr 2008, 5:31 a.m.
Working a calc on soft ground was something I never took into account. Real life is really phantastic! I'd be happy if this explains at least a major part of the keyboard problems. IMO static electricity is another, independent cause of keyboard problems.
I don't know if this is the case, but I always use the HP-35S out of its case, bare on the desktop, and I had some (few) keyboard problems the same.
-- Antonio
I always use my 35S on a desk surface directly with no paper underneath. I still have some flaky keys even with the warranty replacement calc.