We've come across a problem on our farm where old versions of workflows are unexpectedly activating.
As one example, we have a core workflow that has been updated frequently over the last few years. One morning, users suddenly complained about receiving dozens of emails for a single field change. After investigation, we found in the workflow settings page that all of the "Previous Versions" had suddenly been set to "Allow" instead "No New Instances". The single field change was firing an instance for each previous version hence all the extra emails.
Any idea what might have caused this? It has happened on multiple workflows throughout our site. Right now it appears isolated only to 2010 workflows that existed before our upgrade to 2013 (although the workflows were fine immediately after the upgrade).
