about some tricks with time

Hi, there is a question I think about lately:

When I play blitz 3 or 4 times happened to me such a thing:

I have for instance 3 minutes on my clock and my partner 2 minutes . In the next moment suddenly my clock shows 2 min. and my opponent's -3 .As if clocks have changed places.

Do anybody knows something about this trick and how to defend from it ?

Defending against the ol' clock switcheroo maneuver?   

Seriously enough,  let me just say that dealing with laggy opponents is quite normal and this  can force servers to re-compute the clocks suddenly or behave erratically as it did for you. I highly doubt there is anything sinister behind this, let alone people coming up with a defense against it.

Thanks , guys , I think the problem becomes more clear for me now.