Yes, i reported this ([rt.lindenlab.com #395870]), and included a very easy repro. This bug renders spiral ramps made out of tubes or cylinders useless, and you will run into "invisible" walls as you try to negotiate them. I have looked in the "known issues" database and I see no mention of this bug.
These sort of structures are used EVERYWHERE in SL. I personally have verified that the bug occurs in 4 different sims, and affects objects made by people other than myself.
The repro:
Rez a tube
increase size to x 5.0 y 5.0 z 5.0
set 95% hollow
set -0.85 skew
hole size x 1.0 y0.5
Profile cut B 00 E 50
rotation x 270 y 0 z 270
This particular sort of 1 prim ramp is completely borked - you can't even walk past it sometimes.
Spiral ramps made from cylinders are less "buggy" but still suffer form being frequently "blocked" part way up.
Help?!?!?