This has been popping up a couple times recently, so I thought I'd make a sticky.
If you are adding line breaks and spaces when posting and they disappear after you've posted, you've been hit by the "Punctuation Goblin"! (also known as maintenance/upgrades to the site) 
No need to panic, you can get rid of it easy peasy. When logged into the OKP, click on your name on the top left underneath the banner - you will be taken to your Edit Profile page. Click on the Site Options tab. You want to change your Content Editor and Quick Reply Content Editor. In the drop-down menus for both, select TinyMCEWrapper. Save your profile and say goodbye to the "Punctuation Goblin".
If it's extra pesky and still hanging around, PM me or post in Help! with the browser you're using and the operating system you run on so I can help you further.