Found a question here that went unanswered, but I'm having the same problem.
I have a workflow on Opportunity that is set to fire when "created, and any time it's edited to subsequently meet criteria". The Opportunity workflow works well, but has a problem when a related quote's "Start Sync" button is clicked. (The criteria in the workflow is most definitely is not changing from false to true to trigger the workflow, so I have no idea why the workflow would fire. There do not appear to be any field updates or triggers that would cause this to refire.)