Explanation
The services system does not allow multiple drafts
and reports errors when creating new drafts if a draft already exists.
However, if the permissions change on the draft through a different
application using a different API, the user can create another draft
because the other draft is no longer accessible or known. If permissions
change again and the user is given access to the original draft again,
two drafts may appear.
User response
Cancel checkout to delete all your drafts for the
document and then start over by checking out as a draft again. Or
change the permissions on the draft items to hide the other drafts
so only one appears. If the document is not locked, a normal checkout
request should lock the item without creating a draft. Then, cancel
checkout so that all drafts are detected and deleted.