Here's a little test:

<?php
$failDsn = "mysql://foo:bar+@localhost/foo";
$succDsn = array(
                   "phptype"  => "mysql",
                   "hostspec" => "localhost",
                   "database" => "foo",
                   "username" => "foo",
                   "password" => "bar+"
                );
$failDb = DB::connect($failDsn, true);
$succDb = DB::connect($succDsn, true);
if (DB::isError($failDb)) {
    echo "failDsn incorrect?\n";
}
if (DB::isError($succDb)) {
    echo "Hey! are you kidding?\n";
}
?>

It seems that the plus "+" sign in the password field causes a bad parsing on the DSN string.

./configure --with-apxs=../apache/bin/apxs --with-mcrypt --with-mhash --with-xml --with-mysql=../mysql/ --enable-cli --enable-pcntl