PHP5 oddity

This is probably down to configuration, but I'm having an odd problem that I
can't explain.

When I run a script that's extremely simple (creates a smarty instance,
assigns 4 vars with immediate data, and displays a fixed template with 1
smarty tag that's using a plugin I'm working on), I get these errors:

Warning: preg_match() [function.preg-match]: Compilation failed: nothing to
repeat at offset 16 in /var/www/php/includes/Smarty_Compiler.class.php on
line 402

Fatal error: Smarty error: [in t.tpl line 8]: syntax error: unrecognized
tag: translation id="abc" t="hello" (Smarty_Compiler.class.php, line 403) in
/var/www/php/includes/Smarty.class.php on line 1102

translation is the plugin I'm working on, it's in the plugins folder,
amongst all the others, with identical permissions and ownership.

At this point it sounds like something simple like my include path is set
wrong (which is isn't), but here comes the twist: it works perfectly if I
run it from a command line, using the same compiled version of PHP 5.0.1. It
also works fine on a different server with PHP 4.3.8. It's not just the
fatal error that doesn't appear, the warning doesn't either, which makes me
suspect it.

Any ideas?

Marcus
--
Marcus Bointon
Synchromedia Limited: Putting you in the picture
marcus@synchromedia.co.uk | http://www.synchromedia.co.uk