phpcoin and mysql query

Hi,
This maybe off-topic as it is mainly SQL, but I thought I would ask here as I have had many helpful replies from here in the past and also the query is being run from a php script (although examples here are from where I was testing it in phpMyAdmin)
I'm using a piece of software called 'phpcoin' along with the popular 'IPN' mod. I am having some problem with it and have got it down to an mySQL function functioning incorrectly.

This is the structure of the tables involved:

phpcoin_clients:
Field  		Type   		Null  	Default
cl_id  		int(11) 	No  	0
cl_join_ts  	varchar(10) 	Yes  	NULL
cl_status  	varchar(20) 	No  	pending
cl_company  	varchar(50) 	No  	
cl_name_first  	varchar(20) 	No  	
cl_name_last  	varchar(20) 	No  	
cl_addr_01  	varchar(50) 	No  	
cl_addr_02  	varchar(50) 	No  	
cl_city  	varchar(50) 	No  	
cl_state_prov  	varchar(50) 	No  	
cl_country  	varchar(50) 	No  	
cl_zip_code  	varchar(12) 	No  	
cl_phone  	varchar(20) 	No  	
cl_email  	varchar(50) 	No  	
cl_user_name  	varchar(20) 	No  	
cl_user_pword  	varchar(50) 	No  	
cl_notes  	text 		No  	
cl_groups  	int(11) 	No  	0

phpcoin_clients_contacts:
Field  			Type   		Null  	Default
contacts_id  		int(11) 	No  	
contacts_cl_id  	int(11) 	No  	0
contacts_name_first  	varchar(20) 	No  	
contacts_name_last  	varchar(20) 	No  	
contacts_email  	varchar(50) 	No

The sql query is as follows:

SELECT cl_id from phpcoin_clients, phpcoin_clients_contacts
WHERE (cl_email='email@xxxxxxxxxx')
OR (contacts_email='email@xxxxxxxxxx')
AND contacts_cl_id=cl_id

This only returns the client id (cl_id) when the contacts_email is set to email@xxxxxxxxxxx

If the query is just:
SELECT cl_id from phpcoin_clients
WHERE (cl_email='email@xxxxxxxxxx')

Then the result is as expected, anyone have any ideas as to why this is?

Thanks,
Ben
.