More common than you think.
I was once cleared to line up at Leeming only to be told to hold short as there was an unidentified aircraft in the circuit. I waited and watched as a Jet Provost flew a perfect Practice Forced Landing pattern and took off again without making one radio call. No doubt, the controllers at Topcliffe were craning their necks trying to see the aircraft they though was in their circuit.
And in my airline a few years ago, a crew flying from LGW initialised the route from LHR. It took a landing at Shannon to sort the problem and re-align!
Check those tracks and distances!!!!