Here was me thinking you were looking for top of the hour mistakes on either BBC News 24 or BBC World!!
I remember a fantastic one on BBC World back in late 2003. Mike Embley was the newsreader at 1500. The sequence that lead to it was as follows...
1457 - programme finished and breakfiller started
1458 - 3 trails
1459 - 54 second countdown started and cut off when it reached 46
1500 - straight to Mike Embley
Not sure how it happened but the countdown was only 8 seconds long although it started at 54!
Most graphic people would be able to take that capture, stick it in Photoshop and clone in whatever word they wanted, would take me 2 minutes! nothing clever, I'd say almost definately fake.