As the doctors seem to be baffled, it is not surprise to me you haven't gotten any answers here. You may want to try a post on the Heart Disease Community too to see what may come back from there.
http://www.medhelp.org/forums/Heart-Disease/show/72
While not a wide, I do sometimes get a BP reading in which one or the other is too high, but not both. I don't think of that as going in opposite directions.... then too my range is not as high. I am on a BB, Metoprolol to control my HR, so I also get BP lowering. I do not have a history of high BP, but my body adjusts to the BB (I believe) and so my BP tends to run near normal, not too low, as it was when I first went on high dose BB (I take up to 200 mg a day).