You might want to check for any undesirable interactions between "RewriteBase ON" and specifying a iifstatus inquiry path.
StatusInquiry ON /iirfstatus RemoteOK
When I went to myhost.com/iirfstatus, it did *not* pull up the status page (it processed it as if it was an ordinary URL). When I removed the path spec, it worked fine. In version previous to 220.127.116.11, it was working fine with the above directives.
It's probably something really simple.