I've never had the large map auto pop-up on me, including while jousting. I'm not trying to belittle you when I say this, but is there a chance you are inadvertently toggling the (M) button? Or have you reassigned a key in the past that toggles the map? Do you have Carbonite updated?
I right clicked the map and mini-map and picked options and saw nothing that referred to auto pop-up. The only decent suggestion I can make is to open the map options and UNCHECK the first box that says;
"Maximize Carbonite map instead of opening normal map"
If the normal map still pops up on you as Carb's has, then it may not be a Carbonite issue.
Good luck, hope it gets resolved.