En dash in heading title breaks anchor links

Description

Headings that contain en dashes, "--", seem to break anchor links. Example would be headings like hi – lo (with -- between hi and lo), and anchor links of #hi-lo

Steps to reproduce

1. Create a page in Confluence 4
2. Insert lots of content (to generate a vertical scroll bar on the browser during page view) to the page
3. Insert hi – lo (with Heading 1 formatting, and with en dash -- in between hi and lo) at the end of the page content
4. Insert a link with anchor link to #hi-lo
5. Notice that when you click on the anchor link, the page does not scroll to the header. It just stays put. Removing the en dash from the heading though, eradicates the problem

Note that this is only reproducible on Confluence 4.0. Confluence 3.5 produces desired effect even with en dash.