Either two different aircraft using the same Mode S Flight ID (unlikely, but possible), or an instance of the "hex code confusion" bug.
Hello
I would think" hex code confusion" would be unlikely since it normally only affects aircraft that have one or two bits different (these have 5).
AE05AA- 101011100000010110101010
AE0681- 101011100000011010000001
Also I find a lot of military (and sometimes civilian) callsigns aren't what they should be. Whether it is a typing mistake, a 0 instead of O (loganair are bad for this)or a pilot thinking he is being funny by using something vulgar etc. so I suppose it would be far from impossible to get two blue42s at the same time
Andrew