Andrew,

When a drawing including Wipeout entities is stored as DWG it returns back with one vertex less on reloading.

Attached is the same drawing saved as DXF and saved as DWG.

Typically the last vertex is missing in the DWG file.
Does not remove additional vertices on successive reloads a saves.

Don't understand the duplicate end vertices but that could be a solution.
Only, we can't predict if it is going to be saved as DWG in all situations.

Regards,
CVH