search based on select type of item

i’m new in SuiteCRM and I have to say that I’m not very familiar with the build.
What I’ve seen is that the select build by search doesn’t seems to work when you are putting filters like html select type.
For example where I’m using “account_type” in search criteria the select build is:

where ((accounts.account_type in (Customer,Integrator,Investor))) .

What I’ve did :
in SuiteCRM/include/SearchForm/SerchForm2.php
line 790

--$field_value .= $val;
++$field_value .= "'".$val."'";

In this way the query build is :

where ((accounts.account_type in ('Customer','Integrator','Investor'))) 

and the result is like expected.