following my support request inI was told you can't customise theme_pager in template.php unless you remove the angle quotes, or else you'll get empty links.
(code shortened for clarity.)
I also discovered that accents have the same effect.
the solution is to encode the file in UTF-8 (previously encoded in ANSI), but inexperienced people might still have trouble with it. so far I've come across two themes with this bug - Zen and Omega. should I report to their specific queues?