I wrote a sitcom set in a high rise block of flats, which was a bummer because I'd actually written the entire thing and not just a treatment which is what I usually do. Damn you, Sean Lock!
However, a couple of characters migrated over to my latest sitcom effort so it's not always a bad thing. Bloody annoying at the time though.
I've also just watched a clip on youtube of a kids' sketch show that - bizarrely - features a sketch I wrote about 4 years ago and submitted to an entirely different kids show. I don't think it's plagiarism - I'm hoping it isn't anyway - more likely an error? I prefer to give people the benefit of the doubt in the first instance. Thing is I've got absolutely no proof anyway, the original file was lost / binned ages ago, but still, there it is, more-or-less word for word.