Comment 5 for bug 611907

from the POV of the exporter it makes sense to only use a single format, that is able to represent all possible "subgeometries" for simplicity, as long as it is valid (which seems to have happened here, as far as i understand your post).
an importer/viewer on the other hand should be able to read any valid command.

"Be liberal in what you accept, and conservative in what you send."