An error occurred while saving the commentJames Wilson commented
This sounds like the exact problem we had and it's a bug but has thankfully just been fixed in 7.3. Out setup was Office 2010, OnePlace 7.2 & SharePoint 2013 (On Premise). Scenario - open an existing Word document and use OnePlace to save it as a new document. End result - changes are saved to the original document as well as the new one.
v7.3 was released last week and addressed the issue - we've immediately rolled it out and so far so good - no issues reported from our users. Link to the 7.3 release is below. Hope that helps. James