Not an issue for me, Larry, in competition or in the field. The only time it is an issue for me is if I try to compete with a straight gripped gun. I have said before that I do not have as secure control of the gun going into the second shot with a straight gripped gun as with a pistol gripped one. Many have commented otherwise, so it may be just me. But, the heavier the load the more it is magnified, so I think many here who use light loads just may not notice it.
I have never noticed any downward flip with a S x S. I am sure there is a bit of lateral flip, because the barrels are positioned in that manner( side by side). Stands to reason, because there is upwards flip with an O/U, more pronounced with the top barrel as it is farther away from the "center line". But, sideways movement is never noticeable to me. It is there, tho', and regulation takes this into account. If it weren't there, convergence at the muzzles would not be necessary to counteract it.
SRH