When Steam cloud support was disabled (until the compressed save format was implemented in the last update) a few people did use symbolic links to point their savegames folder to a Dropbox folder, to sync saves between a desktop and laptop, etc.
If you wouldn't mind, try moving the profile folder (or just the savegames folder) in the new account and use a symbolic link to point to it on the other drive, and see if that gives the same problem.
