Strange date_modify behaviour? PLS HELP!

[jimdev]

I change one date with date_modify and others that are set to the same value change.

 

It seems like instead of assigning values, = is pointing all these variables at each other? Very odd!

$date = date_create('2009-8'); 
$next_date = 0;
$b = date_create('1970-1-1');
echo 'TEST $date: '.date_format($date, 'Ym')."\n<br/>";
$next_date = $date;
echo 'TEST $date: '.date_format($date, 'Ym')."\n<br/>";
$mod = '+'.date_format($date, 't').' day'."\n<br/>";
echo 'TEST $date: '.date_format($date, 'Ym')."\n<br/>";
echo $mod;
echo 'TEST $date: '.date_format($date, 'Ym')."\n<br/>";
$a = $next_date;
echo 'TEST $a: '.date_format($a, 'Ym')."\n<br/>";
echo 'TEST $b: '.date_format($b, 'Ym')."\n<br/>";
$date = $date;
$next_date->modify($mod);

echo 'TEST $date: '.date_format($date, 'Ym')."\n<br/>";
echo 'TEST $next_date: '.date_format($next_date, 'Ym')."\n<br/>";
echo 'TEST $a: '.date_format($a, 'Ym')."\n<br/>";
echo 'TEST $b: '.date_format($b, 'Ym')."\n<br/>";

 

Expected results

TEST $date: 200908 
TEST $date: 200908 
TEST $date: 200908 
+31 day 
TEST $date: 200908 
TEST $a: 200908 
TEST $b: 197001 
TEST $date: 200908  <-----
TEST $next_date: 200909 
TEST $a: 200908   <------ 
TEST $b: 197001

 

Actual Results

TEST $date: 200908 
TEST $date: 200908 
TEST $date: 200908 
+31 day 
TEST $date: 200908 
TEST $a: 200908 
TEST $b: 197001 
TEST $date: 200909 <---- changes? why?
TEST $next_date: 200909 
TEST $a: 200909 <----- changes? why?
TEST $b: 197001 

 

I have PHP 5.2.8 installed on Apache 2.0

 

Any idea what's wrong here? I feel like an idiot going around in circles.