strange result with copy/paste

I do a lot of pasting, i copy something then paste it like 150 times or so. recently while pasting say “A” then suddenly after about 30 paste it’ll start pasting say “B” that someone else in the room coincidentally copied and pasted on their computer. Has any heard of this and if so why is it happening and is there a way to stop this? This is happening on more than one computer in a network of about 150 computers.