Mining Big Area

Issue I have found which is really is annoying mining in a big area and the miners at times will stop and not continue the mine.

What I mean is I select a 3 tall by 40 lets say and they wont mine it all out. They will just randomly stop and I have to click some of the squres again in which they will continue to mine a few more blocks. I just want them to mine out all the area so I can go do jobs elsewhere.

Maybe this discussion could shed some light on your issue.