MS 101 mono out to stereo jacks noise feedback

Hi. If I connect my new MS 101 to my behringer 6 channel mixer using a mono jack output cable to twin left right stereo input on my mixer I get really bad feedback coming though the speakers. If I switch the cable to mono Jack out to mono Jack in on the mixer its completely fine. I have tried different cables and each time if I use a mono to stereo its gets really loud feedback. Does this sound like a faulty unit? Thanks.