With multipath signals, some reflections or diffracted signal can cancel, and some can reinforce, or anywhere in between. Since the wavelengths are different for two different channels, it's possible that the antenna location is fine for the mess that's coming its way on channel 8, but not fine for channel 10 (shorter wavelength signals won't have the same interference patterns - similar, but cancelling or confusing in different locations).
I'd try moving it up, down, and even aiming it off to one side or the other a bit, as you might be able to cut down on some of the multipath bombardment by aiming it differently. Worth a try, and it's free. Though moving it by many feet (for high-VHF, which has much longer wavelength than UHF) may be what's needed to find a sweet spot.
There's a web site often referenced here with a nice explanation of multipath and its effects that has great graphics, but I can't find it. This is the best I can find.
http://www.hdtvprimer.com/antennas/fixes.html