Same here with my fully-up-to-date 6.3 server.... not sure how long it has been broken as I just had my first ADSL problem since the Version 6.3 machine was installed - and it didn't work... no internet traffic at all when the ADSL went down. Tests showed cable was still up... (One external interface is Telstra Bigpond Cable, the other TPG ADSL2+)
Have restarted my Version 5.2 backup server and now MultiWan works correctly again with my two ISPs... tested to verify
Version 6.3 put on ice for now...