Analysis is wrong for thin-walled structure

[netsonicyxf]

I creat a beam element using a Z shape section, the web of the section is vertical.

Then I apply a vertcal load along the web on the element.

According to thin-walled structure theory, the beam should experience both vertial and horizonal displacements, which is confirmed by a Sap2000 model I created and my .

But Robot only shows a vertical compoment, and this result is different from the result that Sap2000 gets.

The section I use is taken from Australia: Z 100x10, and Steel design-member definition-parameters-thin-walled structure is checked.