I have noticed the following behaviour when a document is under workflow. Can someone confirm if it is a bug or by design ? If the latter what is the reasoning ?

A document under workflow is in the published step, and has a "Publish To" date set to the future. When that date passes the document, as expected gets unpublished correctly. The status icon in the Content tree is "red", and it is no longer visible on site, also as expected. However the header area in CMS Desk still displays :

"Document is currently using [workflow name] workflow and is in Published step."

This indicates that the document is still published.. when it isn't. A client actually noticed this behaviour and is quite rightly confused by it.. I'm looking for a satisfactory explaination for them.. any help appreciated.