Quote Originally Posted by da newt View Post
1) is it written anywhere that casting DM on a caster who is concentrating on a spell DOES or DOES NOT affect the spell? I am not aware of anything written that resolves this question directly. (This is ABSOLUTELY something that should be resolved in the next published rule set.)
I don’t know that anything about concentration is necessarily magical. I mean, in common English, concentrating on something isn’t magical at all (us non-magical folks concentrate all the time), so I feel there would need to be something noting it as different from regular, real life concentration.

Also of note: in the Concentration rules it list what can break Concentration, then states the following:

“The DM might also decide that certain environmental phenomena, such as a wave crashing over you while you’re on a storm-tossed ship, require you to succeed on a DC 10 Constitution saving throw to maintain concentration on a spell.”

So DM is not any of the listed ways to lose Comcentration, nor is it an environmental phenomena, so, RAW, it doesn’t break Concentration.