This problem is addressed in ArcGIS 8.1 Service Pack 1. See Related Information section to download this pack.
ArcMap does not refresh the Table of Contents after you repair a broken link to an image service (if the content of the image service has changed).
If the author of the image service removes a sub-layer from the service before you repair the link, the removed sub-layer will still be listed in the table of contents after the link is repaired. This problem persists even if you close the document and open it again.
Remove the image service from the document and add it again.