Shear force Diagram By STAAD PRO V8i ??

Hi,there

I model a  simple beam by staad pro V8i  the beam has uniform load 2500 kg/m fully beam   and point load 3000 kg act at mid span . when i solve this, but program show shear force diagram at mid span is diagonal line ( act by point load ?). Why not?

 (See Atth. Picture)

Thank you for answer.