It's a Mystery!

We have a mystery on our hands folks! It's the mystery of the multiplying cup!

So in our house we have always had 1 yellow plastic cup - that was until Tuesday when another one materialised in the dishwasher.
Incidentally our dishwasher is broken at the moment (why does this have to happen during exam time grr).
I was washing up (humph stupid dishwasher) and planned on emptying the stuff that was still in the dishwasher to wash that too and saw a yellow cup in there. However, I left the stuff for a while and washed the things on the side which included a yellow cup. I therefore surmised that I must have imagined the yellow cup in the dishwasher as we have only got one. But then I got onto the dishwasher things and opened it again to see that there was definitly another yellow cup in there! Weird! None of us can explain this strange phenomenon but some possible theories that have been mooted (ooo unususal word) are:

1. The cups are replicating so we will soon have a house full of yellow cups
2. The dishwasher broke when it produced a yellow cup through its pipes
3. Yellow cups sporadically (ooo another unusual word) appear from nowhere
4. The cup is actually a figment of our imaginations that's not really there
5. A different cup has changed colour and shrunk
6. The original yellow cup was split into two and it regenerated into 2 whole cups
7. An anonymous donor left a yellow cup in the dishwasher

I guess you are probably all thinking that we are all a bit dumb and have had 2 yellow cups all year but I can assure you that this is not true! Can you solve the mystery?

P.S The sofa obviously didn't like the taste of Beckrum so she has emerged unscathed!