Something strange going on?

When I came home from work (at 10am - I was ill so MrT picked me up) on Friday I had to leave my bike at work in the bike shelter. I've done it before and all was fine. Since I was working away from the office on Monday I didn't check it until I went to cycle home last night. I found part of my bike lock on the ground (the smashed lock casing) and there was no sign of the rest of the lock. My bike was still there, still where I left it but sans lock. All very weird...