Please try using this snapshot:

  http://snaps.php.net/php5.3-latest.tar.gz
 
For Windows:

  http://windows.php.net/snapshots/

This works fine for me:

derick@whisky:~$ php -v
PHP 5.3.7-dev (cli) (built: May  4 2011 09:16:17) (DEBUG)

<?php
$a = \DateInterval::createFromDateString("1 month 1 hour");
echo $a->h; // ok
        
$a = \DateInterval::createFromDateString("1 month 0 hour");
echo $a->h; // ok
        
$a = \DateInterval::createFromDateString("1 month -1 hour");
echo $a->h; // fatal error, ->h is not defined
?>
10-1

please read carefully because DateInterval is really ambiguous
since it is just introduced in php5.3 can be modified before lot of users starts to use this lib

what is ambiguous:

i can do, for example: $datetimeobj->diff($datetimeobj2, FALSE); to obtain a dateinterval with negative values ( read: $obj->h = -1 )

but i can't do DateInterval::createFromDateString("-1 hour");

i don't know how ambiguity will be resolved, but my suggests are:

SOLUTION 1
{

- drop ->invert and allow negative values to ->y ->m ->d ->h ->i ->s

->diff() second parameter works good now

- add a method to dateInterval to invert all values ( ->invertAll() ) that not sets ->invert, but inverts single properties ( $this->h = $this->h * -1; )

- modify constructor to match the new logic
iso8601 seems do not allow negative single values, but can be good to have a constructor like this:
public DateInterval::__construct( string $interval_spec , bool $invertAllValues)
that converts P2Y4DT6H8M in an hypothetically P  -2Y  -4D  T  -6H  -8M

- drop ->add and ->sub from DateTime class and implement ->change that offers same functionality and more when used with negative intervals and positive intervals

}

SOLUTION 2
{

DateInterval properties ymdhis should be always >=0

- DateTime->diff() should not never returns an object with negative values, but should flag inverted intervals using ->invert = TRUE

- drop ->add and ->sub and implement ->change that offers same functionality

$a = DateInterval("P1Y");
$datetime->change($a); // add
$a->invert = true;
$datetime->change($a) // subtract

}

i sincerely prefer the first version because mixing negative and positive single values would be nice (DateIntervall::createFromDateString("1 year 1 month -10 days"))
but i will like any solution that resolves the ambiguities of this class

hi derick, thank you, i will try! read my suggests anyway!!

reopened feedback provided

update: on latest trunk first snippet work good (-1 is obtained)

It's working fine in 5.3, 5.4 and trunk.