Home button opens clock

[Guest Arival]

Every so often instead of the home button returning me to the homescreen it will start to open up the clock application instead, as if it's docked. I can't think of any specific application that caused this to start happening, it just started doing it one day and it seems totally random as to when it it occur. The only way i can get it back to normal is resetting it.

Has anyone else had this, and does anyone have an idea of how to fix it as it's quite annoying!