Probably the WYSIWYG editor is messing with it, try turning it off in profile settings. It's nice but messes with a few other things too.

It does save whitespace though. I don't think the WYSIWYG editor will (although I can't remember) If you mean when you originally create a thread, all the whitespace gets deleted for whatever reason, but resaving the post fixes it. Edit: hmm, no whitespace. I didn't know this. I guess that just shows that it isn't too important anyway, if I wanted whitespace     I         could just    do this.

I don't care if people use the other one, I just don't like looking at the posts of people who use it because it makes it ugly. It also breaks things like this sometimes: ~477820 because of all the p's and  s it inserts, also spans sometimes. In times like this I have to edit their post to fix it, by this time there might be up to 5 layers of p's and spans' mixed in together and it's just a huge huge mess. If I don't delete them all just to fix a single ~, then the post formatting gets ruined, also annoying.