The following wiki-code

h1. Test

h2. heading

h2. header

h2. regular

h1. header

h2. admin-menu

h2. quick-search

h2. main

breaks the CSS for the elements due to the fact that the heading-id is taken from the heading-content.
At first I thought it was a side-effect of the recent TOC-changes (r4376, r4377 and r4379) but after migrating back to trunk@r4264 I noticed the actual cause of the issue.

Here comes the output:

Test¶

heading¶

header¶

regular¶

header¶

admin-menu¶

quick-search¶

main¶