I too would like an answer regarding this function as I am also experiencing incorrect timings. I have switchports that have been in the "Down" state for several years (switch has been up for 4 years plus) and I have just administratively shut the ports down. The "Last Change" counter is stating its last change was back in 2010!?? The Syslog is correctly reporting that the port has changed state but that is useless to me.
I require accurate reports for capacity management so this function is a necessity.
Hopefully this will get "bumped" to the top of the queue again and someone might be able to assist?