Annoying problem with setting out points.

Hi - whenever I set an out point on the timeline, it actually does it 3-5 frames ahead of where I'd like it to go. At the top of the playhead there is a solid black block, the size of which coincides with this discrepency. Have I hit a tickbox somewhere that I don't know about? Or has this always happened, and I'm simply going mad?

Cheers.

On closer insepction I've discovered that it is 1 frame, yup. Has it always done that?