Glo Kobo Glo: Problem with Slider

Hi,

I bought two Kobo Glo's as christmas presents. While on one the slider to turn the reader on and off works like a charm, on the other I have problems in that the slider works only from time to time.

Is there anything that can be done (e.g. hitting it three times on one side...), could this be a software-related problem (both readers have the 2.3.1 firmware), or is it simply a mechanical defect and I have to bring it back and exchange it for another one?

The slider can move from one end of its hole to the other without any obstructions, and there is nothing to be seen from the outside that differs from the other one...

Thanks in advance for any ideas, Joe