There is a leak of execution of free of LOGINREC and DBPROCESS
inside sybase_connet/sybase_pconnet of Sybase (dblib).
This leak occurs, only when it is a system at the high load time,
is that the number of connection of ASE exceeds several times from usual,
and causes the error with the scarce reproducibility of a sybase function. 
A patch like this should work:

Index: php_sybase_db.c
===================================================================
RCS file: /repository/php4/ext/sybase/php_sybase_db.c,v
retrieving revision 1.38.2.5
diff -u -r1.38.2.5 php_sybase_db.c
--- php_sybase_db.c	31 Dec 2002 16:35:36 -0000	1.38.2.5
+++ php_sybase_db.c	13 Apr 2003 13:13:21 -0000
@@ -478,6 +478,7 @@
 			php_sybase_module.num_persistent++;
 			php_sybase_module.num_links++;
 		} else {  /* we do */
+			dbloginfree(sybase.login);
 			if (Z_TYPE_P(le) != php_sybase_module.le_plink) {
 				php_error(E_WARNING,"Sybase:  Hashed persistent link is not a Sybase link!");
 				efree(hashed_details);
@@ -487,7 +488,8 @@
 			sybase_ptr = (sybase_link *) le->ptr;
 			/* test that the link hasn't died */
 			if (DBDEAD(sybase_ptr->link)==TRUE) {
-				if ((sybase_ptr->link=PHP_SYBASE_DBOPEN(sybase_ptr->login,host))==FAIL) {
+				dbclose(sybase_ptr->link);
+				if ((sybase_ptr->link=PHP_SYBASE_DBOPEN(sybase_ptr->login,host))==NULL) {
 					/*php_error(E_WARNING,"Sybase:  Link to server lost, unable to reconnect");*/
 					zend_hash_del(&EG(persistent_list), hashed_details, hashed_details_length+1);
 					efree(hashed_details);
@@ -514,6 +516,7 @@
 			int type,link;
 			void *ptr;
 
+			dbloginfree(sybase.login);
 			if (Z_TYPE_P(index_ptr) != le_index_ptr) {
 				efree(hashed_details);
 				RETURN_FALSE;
@@ -532,12 +535,14 @@
 		if (php_sybase_module.max_links!=-1 && php_sybase_module.num_links>=php_sybase_module.max_links) {
 			php_error(E_WARNING,"Sybase:  Too many open links (%d)",php_sybase_module.num_links);
 			efree(hashed_details);
+			dbloginfree(sybase.login);
 			RETURN_FALSE;
 		}
 		
 		if ((sybase.link=PHP_SYBASE_DBOPEN(sybase.login,host))==NULL) {
 			/*php_error(E_WARNING,"Sybase:  Unable to connect to server:  %s",sybase_error(sybase));*/
 			efree(hashed_details);
+			dbloginfree(sybase.login);
 			RETURN_FALSE;
 		}