OffsetSrf on a simple cylinder in V6 results in a polysurface comprised of two trimmed surfaces. OffsetSrf in V5 on the same cylinder results in a single, untrimmed surface. The V5 result is what I would expect and is more useful.
Options used: Distance=5 Corner=Sharp Solid=No Loose=No Tolerance=0.001 BothSides=No
FlipAll used to change offset to interior of cylinder.
(6.0.17129.11351, 5/9/2017) used.
The attached file has both the V5 and V6 results and was saved as a V5 file. Cyl Offset V5 V6 DC.3dm (63.1 KB)
The attached illustration shows the V6 result after exploding and untrimming. WIP