Hello, I use wordpress-mu-domain-mapping and noticed inconsistencies in the code. The $_SERVER['HTTPS'] is set to either 'off' or 'Off'. I am not even sure why this variable is set, but at least I believe it should respect PHP documentation and use empty/not empty, instead of the IIS' exceptionnal value 'off'.
Also I would suggest to use WordPress core function is_ssl() instead of "manual" detections. Here is a patch for that based on trunk: http://pastebin.com/VqnHarsm