Hi Skip,
I have implemented Cache redirection for 301 errors only which will be Permanant redirection. Expiry header is not expected for 301 direction, so we might not purge it.
RFC 2616 states that if cache is implemented for 302 redirects ( temporary redirects) than Expiry header should be handled and cache purged.

For our change it is not required.

Thanks,
Senthil