I seriously hope this is not a feature, because now at an anvil, repairing/combining anything that is over 40 levels is deemed "Too Expensive". Mojang, I'm trying to act as civil as I can here, but this is a little too much, okay? Why only 40 levels?
The "more expensive" behavior for attempting to repair things over 40 levels is indeed intentional; see Dinnerbone's comments on MC-2307: