Funny you should mention this...

I was just searching here not two weeks ago to see what the opinion was relative to 12/3 multiwire needing tied-in breakers.

Here were some of the results:
https://www.electrical-contractor.net/ubb/Forum2/HTML/000501.html

https://www.electrical-contractor.net/ubb/Forum2/HTML/000586.html

https://www.electrical-contractor.net/ubb/Forum1/HTML/000295.html

https://www.electrical-contractor.net/ubb/Forum1/HTML/001208.html

(Edit was to put carriage returns after each link. Wheeeee!)

[This message has been edited by ThinkGood (edited 09-16-2003).]