Currently the Extrude commands allow the Solid=Yes option when a curve to be extruded is not a closed, planar carve. The command completes and the result is not a solid. This can be confusing to users who thought Solid=Yes means the result will be a solid, not that it may or may not be a solid.
The Extrude commands should be revised so that they:
Check if the curve to be extruded is closed and planar. If it is not then do not offer the “Solid=Yes” option
or -
Not complete and provide a message that the curve to be extruded is not compatible with creating a solid
or -
Complete but provide a warning that a solid was not created.
The first option doesn’t work with preselection; the second might not be extremely useful if several curves were chosen and one or more were not closed and/or planar.