LDAP sync_users problem with SQL

The SQL in the function sync_users() is problematic mysql version 3.23.58 throws an error however it works fine in 4.1.10.

The following is the SQL it tries to execute I've replaced the user idnumber with #FIELD#

SELECT enr.userid AS user, 1

FROM mdl_user_teachers enr

JOIN mdl_user usr ON usr.id=enr.userid

WHERE course=452

AND enrol='ldap'

AND usr.idnumber NOT IN ('#FIELD#')

This code doesn't work however changing it to the following works;

SELECT enr.userid AS user, 1

FROM mdl_user_teachers enr, mdl_user usr

WHERE usr.id=enr.userid

AND course=452

AND enrol='ldap'

AND usr.idnumber NOT IN ('#FIELD#')

is there any reason I'm not seeing for the join? I think the first example (the existing code) is not as portable as the second.