This might be related to what appears to be a bug, reported in a different thread, where MC doesn't see a capitalization change as a data change, so it fails to update. Presumably there is code to not update the database unnecessarily, and presumably this code is doing a case-insensitive comparison, inappropriately.
I found other data-comparison bugs, and all seemed to me to have recently appeared. Another involves incorrect comparison of List-type field content, coupled with MC not saving the changed order of items in the field.