Custom attributes being poluted in DNG 5.0.2 modules?

 We create our modules from templates which include a number of custom attributes. Some of the attributes are pre-populated in the template. Others are empty to be completed at a later time. In some modules the character string "^^http://www.w3.org/2001/XMLSchema#string" (beginning and ending double quotes added) is added to the attributes. This string may be added shortly after the module is created. Other times, the module may have lived for more than a year with multiple baselines taken before the custom attributes become polluted. We've seen instances where there were no other changes logged for the module on a specific date, except for the addition of this string. Is there any record of this behavior, what is causing it, and how to avoid it?