I've also NEVER heard of this! I'd say it's a load of HOOEY! I had 2 of Coda's Aunt's for about 4 yrs. They were from the same litter but looked SOOOOOOOO different you wouldn't think they were even related. Sugar was a calico and Babe was a Siamese mix, both females. They were even feral until they were about 5-6 weeks old. They loved each other! Though they stayed semi-feral. They did end up getting attached to my ex-boyfriend who they still live with. The other sibbling pair I had were Double and Trouble, male and female. The bond between them was so strong that when Double disappeared, Trouble only stayed about a week then ran away (they were inside/outside kitties out on the farm). Trouble missed her so bad he decided not to stay without her.