I've never had trouble with this before, but the last two times I've made baguettes, the ends have curved up while baking.
I have altered my technique in three ways.
First, I'm trying to use a couche more consistently. Previously, I used lightly oiled plastic wrap.
Second, I'm not using parchment paper. My dough goes straight from the couche to the peel.
Third, I've started "tucking" my dough once it's on the peel. It's a little hard to describe, but basically I gently tuck the dough under itself. My goal is to regain surface tension lost during proofing, and to further seal the seam. I find that this prevents the dough from spreading out in the oven.
I don't see how these techniques would cause my baguettes to "grin." Does anyone have a suggestion for how to avoid this?