check_client_access in smtpd_client_restrictions

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I am running postfix 2.6.6 and trying to setup check_client_access using 
a mysql lookup under the smtpd_client_restrictions, which does not 
appear to be rejecting clients when the query returns "REJECT" (which 
has been confirmed to return "REJECT" using postmap -q xxx mysql:..).  
When I change it to look at a hash file with the same IP/REJECT entry it 
works perfectly, so I am wondering is using a mysql lookup not supported 
for check_client_access under smtpd_client_restrictions?