We have recently upgraded from SharePoint 2007, to 2010 and then to SharePoint 2013. In this process we also converted from Classic to Claims authentication. I have verified that both the web application and database have been upgraded to Claims successfully.
Everything seems to be working except the People Picker fields in one List. When I select Edit on any record in the list using Internet Explorer (does not happen in Chrome), it puts an extra "x" next to the existing entry for ANY People Picker field on the form, which looks to be a blank entry. For instance, we have a field "Assigned To", which has a saved name in it (i.e. Joe Smith x. We then have an extra X next to it. The field is set to only allow one entry, which is what we want, but the system is applying a blank entry at the end: