it still rewrites without the SSL virtualhost.
This indicates that apache failed to start after ispconfig tried to enable ssl in this vhost so ispconfig had to do a config rollback and put back the vhost without ssl.
The reason is most likely a wrong ssl key as you use an existing ssl cert. If a existing cert is used, you have to replace the ssl key file of the website with the key that was used to generate the cert. Detailed instructions can be found in the manual chapter 5.4.1.