Try this In AC10:
1 - Using the Object tool, select the L Beams 10 object.
2 - Set the Flange Position to Top and place an instance in the model. (This error only happens in Top position.)
3 - Select the beam and F5 into the 3D window.
4 - Select the beam in the 3D window, go to the Settings dialog, and set Cut. Angle (1) to 45°.
If it works like mine does, the beam will jump slightly out of place and will look like two independent segments, although all the hotspots are still in the right place and the floor plan looks fine. You will also note that the 45° angle is in the correct place.
Does anybody have a fix for this?