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In the third image it looks like a horizontal reference is slightly below the existing geometry. This could start the taper just below the corner rather than right on the corner.
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If the sketch was to the higher edge, the software would have to extend the short edge surface to meet it. Since it is on the lower edge, I expect a similar change is happening, which is what creates the notch.
If there was vertical segment to the sketch that placed the angled edge entirely above the part you would also notget the notch.
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Images re-inserted from original email (they were lost in the migration from the Exploder).