I'm guessing this counts as a feature suggestion rather than a bug, though it does feel like a bug to me.

If you mention someone, they don't receive a notification if they have ignored you. However, if you quote someone, they will receive the notification regardless of whether they are ignoring you or not, which defeats part of the point of the ignore system. It would be good if this could be fixed in 4.3 (or, when this topic inevitably gets buried, whatever the next release is when you read this).

This sounds like a bug on the surface. I've added it to our internal tracker to have it looked at.