The replacing of dash with colons didn't seem a good idea, cause for the Lenovo's it worked like that. Only the Dell's were the reluctant ones, so it seemed to be a station configuration problem.
I have several teaching rooms with two master computers in operation. It is important that each master computer needs its own private key. I.e. the students' computers each get a public key of Master 1 and Master 2. Master 1 then has its own private key, Master 2 too. A private key for both masters does not work.