Odd Unbalanced Force at edge of the liner

Hi, I am calculating vertical foundation bearing capacity by using the Liner as the stiff foundation, and apply specified velocity along the middle line, as can be seen from the 1st figure below, where half foundaiton is modelled. The bearing capaicty can then be calculated by summing the unbalanced force from the nodes where the velocity was specified. The total unbalnced froce (reaction) appear to be correct. However, the force vector at the outer edge is odd, and pointing upward (see the green arrows on the 2nd figure, and more clear on the 3rd figure, where soil has been de-activated and the liner been rotated). Does anyone know the reason? Note that the soil stress distribution seems to be correct.
I suspected there was something wrong with the liner/shell elements when it comes to the element at the edge. This is something I raised before (but was not solved) when I was looking at the soil-liner contact pressure for the liner being embedded in the soil.

It is hard for us to comment what occurred without the datafile. Could you please send the datafile to flac3dsupport@itascacg.com so that we could duplicate the issue?

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