I have a stack of 2 x 3750's (1= master, 2= member).
Both have 2 stack cables attached. I added a third 3750 and unplugged one of the stack cables from switch 2 to and connected to switch 3. So my cabling was 1 - 2 and 1 - 3.
I hadn't added the 'switch stack-member-number priority' command to the new switch as I was planning on doing it later but thought I'd hook it up in the mean time.
This seemed to cause a problem with my master switch which went offline as if it had detatched itself for the stack and switch 2 became the master.
Removing the new switch and reloading seemed to rectify this. However I wouldn't expect adding a dormant switch to do this? Can anyone advise me on why this may have happened.