According to a post on shortwave DX blog (shortwavedx.blogspot.com)

https://www.blogger.com/comment/fullpage/post/28488709/1271878935623426448

Coast (relay) have been heard on 2 AM frequencies simultaneously in the past day, 1575 and 1593 kHz. I assume both are not from the same transmission site, otherwise I'd expect there would be serious mixtures (IPs) radiating on 1611 and 1557 , not technically feasible to filter out (to quote an American DXer - "Leapfrog mixing")