[pear][interbase] strange interbase problem caused by non-db code...

i have a strange problem that's making me crazy... i have a php script which gets data from an interbase db and show them to the user and in the same page i have some calls to functions in other scripts that draw me some common forms (to select what record user want to view); one of this functions creates a combo with a list of month / year to select what month the user wants to show. this function has a row where i actually get the date of a month from another function and i print it out using strftime, just as below

     $sMonthList .= strftime("%B %Y", DateAddMonth(getdate(), $i));

with this script, i get this error: Warning: ibase_fetch_object(): supplied argument is not a valid InterBase result resource in c:\programmi\network\php\pear\DB\ibase.php on line 192 but if i change the above code in this way

     $sMonthList .= strftime("%d %B %Y", DateAddMonth(getdate(), $i));
the error doesn't fire and all the script work fine (except the combo with month / year which does not display as i want).

can somebody explain me what's the matter between the error and the strftime? Since the same error occurred to me randomly several time, it seem the php/pear does not like text disposition of my code... sometime i solved the error simply moving some lines of code in other position within the script... i don't think it's a normal way. Thanks in advance Phelipe de Sterlich