I have upgraded both my Semcycles with higher quality seat post clamps in
an attempt to avoid the seat-twisting and -lowering problems I have
encountered. I cut off the stock stamped steel clamp and used GT
double-bolt BMX style clamps in their place.
It wasn't too hard to do and I haven't had any problems of that sort since. I submitted an article for ON ONE WHEEL describing the process but it may or may not be published. If anyone is interested I will email them a copy (or post it here if enough people ask) and try to answer any questions that may arise.