I have been having issues with Rhino viewports lately. The issues start to manifest in simple 2d drawings (and are magnified with surfaces themselves when selecting them in shaded mode, though that might be a separate issue).
You will see in the first attached screen shot where I have a simple drawn shape and I offset it (not deleting the input). Then, both should appear, but only the offset does (shown in the second picture). Then, when I rotate the viewport the original curves show up again. Does anyone have any suggestions?