Is this just with one particular save game? Or any new game you start too?
IM saves are no different from non-IM saves, does it happen to both?
Please do a full **clean** re-install:
- move any valued save games elsewhere
- "uninstall" in Steam-CK2
- manually delete both the Steam/SteamApps/common/CK2 AND Documents/Paradox/CK2 folders
- re-install game in Steam, run a Steam Verify when done.
- start the game with no mods active and test
In particular make sure there are no files or folders left under either the Steam CK2 or Documents CK2 locations, before installing again.
**File Locations on Mac OS X**
The executable and DLC folder are in Users/USER/Library/Application Support/Steam/SteamApps/common/Crusader Kings II/
On OS X 10.8.x and later, Apple have hidden the /Users/USER/Library/ folder. To see it go to the Finder, hit command-shift-G (ie Go To) and type in ~/Library/ .
The user files (settings.txt, error logs, saved games, gfx, mods) are in /Users/USER/Documents/Paradox Interactive/Crusader Kings II/ .