No two choices should have the same ID

We've been experiencing an issue with adding existing site columns to a SharePoint list. We are able to add existing site columns using SharePoint Designer, but can't do so using the web front end.

The error we get is:

Getting Error Message for Exception System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.InvalidOperationException: Failed to compare two elements in the array. ---> System.ArgumentException: No two choices should have the same ID at Microsoft.SharePoint.ApplicationPages.ChoiceComparerWithDefaultGroup.Compare(PickerItem c1, PickerItem c2) ...

I tried following the steps listed in this blog (http://sharepointdiva.wordpress.com/2012/08/16/no-two-choices-should-have-the-same-id/), however, there are no columns that have the same underlying ID. We do have columns that have the same display name but have different ID's and internal names.

Has anybody experienced this before?