rs.IsObjectSolid() is reporting False for closed extrusion objects. To test, make a solid box (as an extrusion) and run the following on it:
import rhinoscriptsyntax as rs
ext=rs.GetObject("Select extrusion object",1073741824,True)
print rs.IsObjectSolid(ext)
The above returns False here in the current SR11 RC 6.0.15013.11341
There is a youtrack item for a old bug that says this was fixed and closed for SR10 in October of 2014:
http://mcneel.myjetbrains.com/youtrack/issue/RH-28865
@piac Maybe it got unfixed somehow…
It seems to be working correctly in the Rhino WIP.
—Mitch
Edit: the vb Rhinoscript Rhino.IsObjectSolid is working correctly…