Another the same problem, I've tried to write a script that cleanly reproduces what happened:

<?
   $dblocation="localhost";
   $dbname="mydb";

function TryHere () {
   global $dblocation, $dbname;
   $database=pg_Connect($dblocation,"","",$dbname);
   $datein=pg_exec($database,"select datetime 'now';");
   pg_Close($database);
   $file=fopen('/tmp/some.file.txt','r');
   if (pg_NumRows($datein)) {
      $row=pg_Fetch_Array($datein,0);
      echo "Date is: $row[0]<br>\n";
   }
   fclose($file);   
   #
   # Everything worked fine
   # 
} 

function TryHereAgain () {
   global $dblocation, $dbname;
   $database=pg_Connect($dblocation,"","",$dbname);
   $datein=pg_exec($database,"select datetime 'now';");
   pg_Close($database);   
   if (pg_NumRows($datein)) {
      $row=pg_Fetch_Array($datein,0);
      echo "Date is: $row[0]<br>\n";
   }
   #
   # Mmm... Not anymore :(
   #
}

   TryHere();
   TryHereAgain();
?>

If I ommit to open a file, or to use any of the pg_NumRows or pg_Fetch_Array at the first call of the routine everything is ok. Also if I do the same things, but without functions. Quite interesting...