Interesting... OK, I'll try. But I tried on two other guards as well, and they did the same thing, so it'd be pretty coincidental. (Also, what's a checkpoint in this context?)
Edit: Huh, you're right, moving away worked. If both the guard and I are in a certain area, he'll drop the item, but we're safe if only one of us is in the area. The top of the clock tower is also broken in this way.