This is an issue we have been dealing with for several years. We have a 2 week window at the end of the fiscal year where users can create documents for either the new or the old year. Invariably, a document is created for the "wrong" year and the user discovers this after it has been saved as complete. When they go back into the document and change the posting date to the other fiscal year, SAP interprets this as a new document and triggers the completed event multiple times resulting in multiple workflows for the same document. Users can simply approve the workitems and the additional workflows will error when trying to post and I delete the extras but apparently this has become an unacceptable solution.
The events are triggered simultaneously and I can't figure out a way to get rid of the extra workflow instances. Any help is greatly appreciated.