When I Alt-Shift-Drag an object, to duplicate it whilst constraining it to horizontal or vertical movement, often the duplicated object jumps far away to move against the canvas edge instead.
It seems to happen when Alt-Shift-Dragging an item without first clicking on it to select it.
I can replicate the bug by creating a new shape, clicking away to deselect it, then Alt-Shift-Dragging it. Here’s a screencast: http://recordit.co/uYIAEgNL7I As you can see, constraining works fine if the object is already selected, but not if it was deselected at the point when I started dragging.
What you are seeing here is intended behavior of the Smart Guides in OmniGraffle. It’s aligning to the last items you placed based on your previous selection. Depending on what is selected, Smart Guides help you align your objects to one another by default. Since you’ve duplicated the currently selected item, you’ll notice the new item is showing smart guides to help you align it to the existing shapes on the canvas. If you let go of the shift key, you will stop being restrained to the objects smart guides are comparing against.
When a feature doesn’t work like Sketch in OmniGraffle, that doesn’t mean it is neccisarily a bug. While some of our features do overlap, not all of them are intended to work the same, and there isn’t an intended one to one match. If you see any behavior that doesn’t make sense to you, feel free to email us questions and we will help explain where there are differences based on features, or if there are differences because OmniGraffle is behaving in a way we don’t expect. We will let you know also if some of the differences are known issues or new bugs that you reported.
I accept that it behaves as designed, but I do hope you ask yourselves whether that is indeed the most useful and expected behaviour.