Hi Alain,
Sorry, I'd lost track of this. I'm using the OAuth2 Ruby gem to pass do make the request, but I'm constructing my own URLs/bodies outside of that, and parsing the results myself. I've been unable to duplicate the issue through the API Explorer.
I've seen the issue a lot less than when I first posted this (no changes to my code though), and I don't have the exact log available. If I see it a bunch more, I'll tack on the exact request to this thread. In the meantime, just looking at my code:
POST
Authorization: Bearer tokenstuff
summary: "Name of Calendar"
So pretty vanilla.
-Isaac