Fishless cycle reversing itself?

[Def]

So here I was thinking I'd do a fishless cycle on my quarantine tank with mature media to get it up and running. I personally am not a big advocate of fishless cycling, I'd rather do it au-naturelle with fish and a bottle of Cycle. Anyway, that's another story.

I sucessfully cycled the 10g quarantine tank in about 7 days, adding a few drops of pure ammonia showed it (and nitrite) was completely consumed within 24hours. So then I had all that trouble trying to get hold of a gold nugget - in the meantime, I kept using a few drops of pure ammonia to keep the bacteria happy and the tank cycled.

All was good, ammonia 0 and nitrite 0 until I tested today. I put a few drops of ammonia in the tank a day or so ago, so I figured I'd double check the readings this morning before I go and get the nugget. Hey presto, ammonia is showing at about 1.0?!??!??!

Anyone have any ideas how come the cycle seems to have restarted itself? Nitrite is still showing at 0, but that may be a false assumption on the basis that ammonia has been present and not consumed for 24hours +.

I'm getting a bit hacked off with this, and I really don't want to have to wait another week or 2 if the cycle really has restarted...