Commented Unassigned: Renaming a custom field changed all issue values [171]

I have a drop down list custom field that has contains a list of all my clients. Every issue is required to have a client assigned. I went and renamed one field in the drop down list, and all my issues have been reassigned to that custom field. I now have to go through ALL of my issues and reassign them to the right clients!
Comments: I have had to go through 400+ issues in one project and reset the custom field values to the correct setting. Can't believe something like this could happen :(