Here’s a slip-up (or two or three) that went unnoticed by the brain trust at Yahoo! Style:
I don’t know if a slip-up (which, as a noun, requires a hyphen) can backfire, since a slip-up is an accidental mistake and backfire is usually reserved for conscious errors. But I’ll let that one go. What I can’t let go is the last sentence in the paragraph. What the heck does that mean? I think it means the writer is unfamiliar with English.