Entering more than four lines of text in a comment field hides the wiki preview and help icons

When you enter more than 4 lines in a comment field it hides the wiki preview and help icons, and the comment security settings padlock floats into the text field.

Cancelling and adding the comment again keeps the field as is. You need to refresh the page to clean it up.

See screenshots.

FF 3.6 on OS X.