Weird, didn't notice the PHB and SRD versions were different (the SRD is missing the flesh to stone example). I'm with Vegepygmy with his statement that the former trumps the latter as authoritative text. I'm not sure if I understand propsero63 though: Is he saying that, per the PHB, that flesh to stone would not be affected? I believe it is (and the PHB seems clear to me on that point and the latest FAQ backs that up).
I agree w/ frankthedm in the fact that the spell doesn't have to specifically say it cannot be dispelled by dispel magic to be effective. However, we do have a diagreement on the instaneneous part. Again, if flesh to stone is our example, it is clear that is is instantaneous, and thus dispel wouldn't work. Its also greater than 5th level. So, we ignore the PHB example, that would mean it could be affected by break enchantment. However, it seems clear from the FAQ and the PHB example that break enchantment can break flesh-to-stone. Thus, my reading is as follows:
- If the spell to be "broken" specifically says dispel magic cannot affect it, break enchantment only works if it is 5th level or lower.
- If the spell doesn't say so, but is not valid target due to *only* the fact that is it instantaneous, than it can be broken.
Essentially, the "instantaneous" factor not long applies. Thus, insanity could be "broken"
That'd be my ruling baring something more official. Is it game breaking? Not really. By the time something can cast insanity on you, you (should) have access to heal.