Pvt. Winslow
Explorer
[MENTION=2011]KarinsDad[/MENTION] here is something.
At our table, we interpret the "source of damage" wording to be per creature, as in a creature is one single source of damage. If a Dragon was to breath on you AND claw you, that's one single source of damage (the Dragon) so you only make one concentration roll.
If your DM interprets a source of damage to be a type of damage, or even worse, each attack, you are statistically speaking going to fail a lot more concentration rolls (until your bonus is +9 at least). I personally don't think that's the intention of the rule, but the wording is ambiguous.
Only issue I could see with this is if it was reversed and used on the PC's. The next time they fight say a monster caster with ability to use Stoneskin, they might be peeved if they only force a single concentration check per turn of actions, even if they hit the creature three times each.