The CEON URI Mapping module must use the site root "/" as cookie path to work properly. My Zen Cart resides in "/purchase/". Unfortunately, when setting cookie path to root, customer login doesn't work in my case - the session is simply wiped when attempting login. Writing out session data with file_put_contents() reveals that the session is wiped after calling PHP header() for the redirect after login (/includes/functions/functions_general.php line 46), but before arriving at /purchase/index.php. Not sure how to do further troubleshooting.

Just in case, here are my admin session settings:
Session directory => /path/to/root/purchase/cache
Cookie domain => true
Force cookie use => false
Check SSL session id => false
Check user agent => false
Check IP address => false
Prevent spider sessions => true
Recreate session => true
IP to Host Conversion Status => true
Use root path for cookie path => false (but overridden by CEON module)
Add period prefix to cookie domain => true (setting this to false made no difference)

Any ideas what's causing the session reset and/or suggestions for how to troubleshoot further?