WordPress忽略'％'字符

I'm experiencing weird WordPress behavior. There are some functions like comments_popup_link, which are supposed to provide different text for 0, 1 or n > 1 occurrences of some object (ie. comments). Codex states, that in "many" version of text, one should put % (percent sign) as a placeholder for numeric value. Example says:

<?php
  comments_popup_link( 'No comments yet', '1 comment', '% comments', 'comments-link', 'Comments are off for this post');
?>

When I mistakenly replaced % with &, everything worked correctly:

<?php comments_popup_link('Napisz komentarz', 'Komentowany 1 raz', 'Komentowany & razy'); ?>

However, when I fixed my mistake:

<?php comments_popup_link('Napisz komentarz', 'Komentowany 1 raz', 'Komentowany % razy'); ?>

WordPress suddenly started ignoring what I entered and used its own text instead:

Why does it happen? How can I fix it? I have exactly the same problem with other functions like one mentioned.

For the record, sample from Codex doesn't work as well.