Changing option group values not updating existing data values

I've noticed that changing values for options inside of options groups does not lead to values being updated for existing data. I'm assuming it should be doing this.

Can replicate on: http://drupal.demo.civicrm.org/civicrm/

• Open any contact
• Set their "Preferred Method(s)" to all values
• Go to the "Option Groups" administration page
• Open the options for "Preferred Communication Method"
• Edit any of them and change the value to something else
• Go back to the contact and you'll find the option to changed unselected.

Or another example (more serious in my opinion as it's just a single value selection, so shouldn't be as difficult to update existing values):

• Open "Constituent Information" for any contact
• Select "Education"
• Go to the "Option Groups" administration page
• Open the options for "Most Important Issue"
• Edit the "Education" option
• Change the value to something else
• Go back to the contact you selected "Education" for before, they now don't have anything selected.

For the time being of course I can just make sure we don't change the values of any fields, but overall this seems like a pretty serious bug, over time we've changed the value of quite a few custom option group values which have had this issue.