Ok right, this is not something new its to do with aircraft which have a faulty GPS link to there transponder, this means there position suddenly jumps from one place to another (300miles +).
RadarBox plots it and you might see lines like that untill the aircraft goes out of reception.
Rumour around and I think there are some posts in this forum that some Learjet's do this delibarately to spoof there position so they can't be tracked well.