It was a little thing, but it bugged me with CommunityServer.

I could never include HTML or JavaScript in a specific post. Some HTML worked, other HTML just got stripped out (had driven my mad trying to style images initially.

I'd posted on the CS forums but not had any luck until I found this answer which basically said I should have RTFM in the first place!

Of course the functionality was as designed, and (of course) there is a way to fine-tune it. In this case in the <markup> section of the CommunityServer.config - it allows you to specify what tags and parameters are valid (and any not on the list simply get converted to safe markup. It's very clever. And just goes to prove I really should try and find more time in the day to read manuals!