I just experienced the following bug:
- I have crafted some dragon gear
- I put on my fortify smithing items
- i am now able to improve a dragon plate BP to 169 armor.
- i put on a full set of plate dragon armor that i just made, not enchanted.
- i am now able to improve that dragon BP tot 212 armor ?????

The dragon armor has no fortify smithing enchantments on it, so it should not make any difference in the effect on improving armor! I reported a bug earlier with a orcish gauntlet. Maybe there is a bug in the heavy armor skill that affects smithing ?

p.s. i think i have worked out why this happens: I have the perk "heavy armor - > Well fitted" to give a 25 % bonus to armor. I have verified that removing any of the four pieces of heavy armor i was wearing will reduce the armor rating of the improved armor. IMHO knowing how to wear armor and knowing how to improve it should be two separate issues though.