You will need to disable the Client autoconfiguration feature before you can configure reverse proxy mappings. The Client autoconfiguration feature is for the forward proxy operation, not reverse proxy.
The Virtual Multihosting feature establishes automatic reverse mappings. Do not create reverse mappings for mappings that you provide using the Virtual Multihosting page.
Virtual mappings are specified with virt-map function in the obj.conf file.
Virtual mappings are matched in the order specified in the obj.conf configuration file. If regular, reverse, regular expression, or client autoconfiguration mappings appear before the virtual mappings, they will be applied first. Similarly, if no matches are found in virtual mappings, translation will continue to the next mapping after the virtual mapping section in obj.conf.
In the order of specification, reverse mapping should appear before other mappings.
If the port number of the proxy server is changed, you will need to recreate the Virtual Multihosting mappings, to reflect the new port number.