Moscow mystery

Have a friend who is living and working in Moscow at the moment. Her birthday is at the end of November so I sent her a small present and card to her work address copying it from her email signature.
It never arrived.
Stolen I thought.
Then yesterday it turned up in my office, in London, card and gift opened but intact. The return address I'd put on it was my home address.
So where has it been for the last five months?
I know it's been bouncing around south London for a while because of the scrawls of different postcodes written on it. My return postcode was a little unclear and, as I'd reused a padded envelope, a postman with initiative had partially ripped off the Moscow address to reveal the original label which was to me at my work address.
But there are no clues as to whether it got to Russia and why it came back.
Once I received a postcard a friend had sent while on holiday in Italy a year after she got back.
Is it a case of it maybe falling down behind the sorting bench and being forgotten about until someone decides to do a thorough tidy up or do posties play postal roulette and if the bottle stops on your package it get lobbed in the corner for six months?