I presume you are tunnelling the HTTPS using the HTTP "CONNECT" method?
If so, the HTTP state parser doesn't support that - once the connection becomes HTTPS it will be unable to parse the traffic flow and will give up, in a somewhat inelegant manner.
What you'll need to do is selectively disable the HTTP parser once you see a "CONNECT" method in the stream, and leave it disabled for the remainder of that TCP connection.
You'll want to look into the HTTP::disable and HTTP::detach commands from memory - let me know if nothing comes up searching here and I'll dig out an example I have from a while ago.
--
Aaron