If a hash '#' symbol appears in a URL posted in a comment on Brickset, it does some bizarre things to interpret it, breaking the URL into three parts and applying each part separately to each chunk.
Noticeable because LEGO IDEAS uses hashes in its URLs. And also their server is a bit cheap and doesn't decode %23 as a hash either!
So, for example, this summary of everything on IDEAS with a 'classic space' tag:http://ideas.lego.com/discover#search/f:tags=classic space/s:most_supported
gets turned into a mess where the bit before the hash is one url, the hash itself is another, and the rest a third - none of which are valid.
If you try to edit it, you see the HTML code. But edit that, give it some valid HTML, and it converts it to the mangled version again.