These aren't mis-prints at all and aren't particularly rare.  I believe they were produced for the Maltese market but I could be wrong there. There are lots around and I have quite a few. They are a bit annoying, especially when you are trying to get a loose set together and someone sells you a load of them without telling you about the backs. Whenever anybody buys any from me I let them know so they have a chance to say no.

They are better then the Yugoslavian stickers which are dreadful quality and should be avoided at all costs.