Mapping Domain Issue

Hi..i have a issue at the subsite domain mapping..
1. Main site is a SSL https
2. Subsite automatic detacted https. So domain mapping to subsite also detact the https
example:
-My main domain: https://www.mydomain.com
-Subsite domain: https://www.mydomain.com/subsite. Mapping to: http://mappingdomain.com
so..this domain still redirect to https

Any body help me..how to fixt this issue..