Description:
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When i try to connect to Mssql I randomly encounter warnings with "unable to init stored procedure".

Whenever i try to run the query seperatly in Microsoft SQL Server Management Studio Express the query never fails, so i don't think this is an SQL-server problem. 

When i refresh the website often i can see one time it returns a resource (which is good) 'resource(92, mssql statement)'
or a warning 'Warning: mssql_init() [function.mssql-init]: unable to init stored procedure in /var/www/html/test/app/controllers/TestController.php on line 40'

That TestController sets up a persistent connection and initializes a stored procedure. That's it, nothing more nothing less.

The expected result en the actual result keep randomly appearing

Reproduce code:
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$a = mssql_pconnect($server, $username, $password);
var_dump($a);
var_dump(is_resource($a));
$b = mssql_init("dbo.$procedure") or die(mssql_get_last_message());
var_dump($b);

Expected result:
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resource(91, mssql link persistent)
boolean true
resource(92, mssql statement) 

Actual result:
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resource(91, mssql link persistent)
boolean true
Warning: mssql_init() [function.mssql-init]: unable to init stored procedure in /var/www/html/test/app/controllers/TestController.php on line 40