Type specific custom fields lost when issue type is changed

Custom fields that are added that only apply to a certain issue type are lost when the issue type is changed. For instance, if there is a custom field called "custom1" that is only listed for issues of type "bug", when the user enters values into that field AND changes the issue type to something else, the newly entered values in "custom1" are lost.

This is a somewhat tricky but perfectly feasible scenario. Possible solutions:

• Warn the user when changing an issue's type if there are any custom fields that will be lost?
• Save the user's values before changing the issue type, even though those new values won't be visible in the new issue type view?
• Create a new issue with the new issue type (with a special relationship to the original issue) so the old values aren't lost?

Just some thoughts.