Seriph
Probably running at more than a couple PER day at the moment. Unauthorised abscence from the frequency is now a mandatory MOR offence by ATC, as well as pilots involved running the risk of some unexpected formation flying.
Usually turns out to be finger trouble, or selecting an incorrect frequency. We're all human after all and all make mistakes so it's going to happen. Bone up on your interception procedures folks, and make sure you don't go too fast for the Tornados !!!