bath room stains

I have a customer with a problem I have never seen before. She is getting red stains (Like droplets ) occurring on her bathroom ceiling. From a clean ceiling after cleaning with a bleach solution the stains appear after about 48hrs. Looking like normal condensation but leaving red crystals after drying.

House is normal construction under shingle, bathroom has window and customer says she always keeps it open. Inspection above bathroom reveals nothing unusual and no dampness or normal signs of mould. So have you seen any thing like this , I have looked on Internet but found nothing like this. We live in dry area of southern california.