I assumed it was the router messing around but the whole os became horribly laggy and slow, verging on non-responsive at the same time - which made me think it was software based.
In that case, it has to be the Mac. Sounds like a serious bug.
After commenting on how stable TM was, its getting on my nerves. I plug in the drive, it then takes ages to do a backup and gets stuck. Done it a couple of times now. Gets on my nerves.