The issue service update method should allow you to update a single field without over-writing existing field values

Currently the issue service update method expects all fields on the edit screen to have its values re-submitted when called. This is how the HTML interface works and thus is the way the fields expect things to work.

From an API level the issue service is more useful if you can set just a single value and update an issue without over-writing the existing values. This is what the SOAP interface does at the moment.