When you do an update with the Zend\Db\Sql\Update class and you use the where function to give a clause, if you pass the clause as an array, only the last entry of the array is used.

Steps to repoduce the problem:

use Zend\Db\Sql\Update;
$update = new Update('table');
$update->set(array('fld1'=>'val1'));
$update->where(array('id1'=>'val1', 'id2'=>'val2'));
print ($update->getSqlString());

This code produce the following sql request:

UPDATE "table" SET "fld1" = 'val1' WHERE "id2" = 'val2'

instead of

UPDATE "table" SET "fld1" = 'val1' WHERE "id1" = 'val1' and "id2" = 'val2'