I found an old thread that discusses this oddity.
Why don't "Change Case" edits show during "Track Changes" | Microsoft Office Forums

The suggested workaround solution was to keep two copies of the document (a before and after version) and then compare documents to see the tracked changes.

It would be possible to code a solution more localised than that document-level workaround but it sounds like a fair bit of work for not much in the way of perceived value.

__________________
Andrew Lockton
Chrysalis Design, Melbourne Australia