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The ecliptic is tilted, but it never flips over itself, so the only time the sun and moon are at the same azmuth is during a new moon. 6 hours away just means they are 90 degrees apart in azmuth and that is only loosely connected to when they will rise or set. What it does mean is that if the sun is due west right now, the moon is due south right now and 6 hours from now, the sun will be due north and the moon due west. But depending on the tilt of the ecliptic for your season and location, the sun, the moon, both, or neither may be up at either of those times.
For example, first quarter is this Saturday. 3 hours or so after sunset (9:35), the moon is at an azmuth of 251 degrees and the sun at 294. The sun and moon both trace out the entire azmuth circle in a day, with the sun chasing the moon for half the month and speeding away for the other half.
What people are noting is the tilt of the ecliptic. Once a day in the middle latitudes, the ecliptic is near vertical on each side of the sky, with the times dependent on the season. So when the moon is on it in that part of the sky at that time, it is laying on its side. And this can happen in any phase and happens every month at a different time and in a different phase. Here's the view last night (ecliptic near vertical) and August 5 (nowhere close to vertical), both times a little less than 5 days past new.
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Got this from a forum I found searching the subject.
http://www.physicsforums.com/archive.../t-203670.html
I guess it makes sense what is said there, since the sun kinda rotates clockwise over the sky here, it will eventually shine at the moon from "below" the earth compared to us in the north. Therefore, when the conditions are right the moon will appear horizontal.
It's only really visible at new moon and can happen at different times each time.