ob_* problems using wp-load and query_posts() outside WordPress

I wish to display specific posts outside WP in my own app.

I’ve made a simple PHP testapp that does this and works great, HOWEVER…
my real app uses a trailing edge but quite functional templating system depending on string substitution, so the default behavior of echoing the content at the point of the call doesn’t work.

Solution: use the PHP Output Control Functions. HOWEVER…
my template object is trashed afterwards.

define('WP_USE_THEMES', false);
require('../wptest/wp-load.php');
query_posts("p=289");
$this->template->set_var("TITLE", 'test4');	 // templating object working normally
ob_start();
	while (have_posts()): the_post();
		the_content();
	endwhile;
$myStr = ob_get_contents();
ob_end_clean();
$this->template->set_var("TITLE", 'test5');	 // templating object is trashed with:
// "Fatal error: Call to a member function set_var() on a non-object ..."

any clues on how this messes up my template?
Oh, the ob_ code DOES work – my post IS correctly in $myStr, ready to use if only my template object was intact! ??