Session database errors and query builder chaining

I am having an issue on production server after upgrading to CI3. Additional conditions are being added to a session database query by the query builder. The two where clauses in bold are from a simple select query in an normal CI model, and I am not sure why they are being applied to an update query within the CI_Session_database_driver class. My suspicion is that because these session handler functions are registered using PHPs session_set_save_handler that they have access to the CI->db object that is concurrent with other running processes. Any thoughts on resolving this?

A Database Error Occurred
Error Number: 1054
Unknown column 'ur.user_id' in 'where clause'

UPDATE `ci_sessions` SET `timestamp` = 1429568240, `data` = '__ci_last_regenerate|i:1429564536;'
WHERE `ur`.`user_id` = '1'
AND `r`.`active` = 1
AND `id` = 'efe35de70aeeab890cb68562d8058cad6e48d52b'

Filename: libraries/Session/drivers/Session_database_driver.php
Line Number: 243