imap_headers() should return array of headers of e-mail
messages. Each header should include date field. This is
code from ext/imap/php_imap.c imap_headers function:
                mail_date(tmp+11, cache);
                tmp[18] = ' ';
                tmp[19] = '\0';
                mail_fetchfrom(tmp+19, ...
So, only 7 chars are reserved for date.
But this is description of mail_date() from imapd-4.5 :
     "This function accepts a message cache element that contains date information, and writes an IMAP-4 date string, that is, one in form:                      
        dd-mmm-yyyy hh:mm:ss +zzzz "

So, date field in header string looks like 
dd-mmm- ( 20-Jul- , for example )

Possible solution: 
	mail_date( tmp+11, cache );
	len = strlen( tmp );
	tmp[len] = ' ' ;
        tmp[len+1] = 0;
	mail_fetchfrom(tmp+len+1 ...