Crunchie crust

I have a question about others experience with crust. I have made several batches of Rustic Bread (excellent recipe by the way). I have found that when my bread comes out of the oven it is nice a crunchie crust, but as it cools it often becomes soft until fully cooled at which time some cruch returns.

I have been baking on a stone in 450F oven with steam.

Anyone with a similar experience? Is this what to expect as the bread cools?

JM