How to prove this error.
First create a square on the screen in Xara 10.
Color it blue.

Copy & paste this square. Change the copy's color to green.
Copy & paste the green square. Change that copy's color to red.

Select the green square and the red square. Do a BLEND operation from the green to red squares. Select the blend group, CONVERT TO EDITABLE SHAPES. Then UNGROUP the blend.

Now for the Color Picking Error Bug.

Rectangle Select the line of blended color squares.
Click the COLOR PICKER eyedropper icon, drag the COLOR PICKER eyedropper onto the blue square. Have all the selected squares changed to blue? Why not? A list propagation error (count 0 to ten, but only run the loop from 1 to 10 or from 0 to 9).

Was working on a business card that I needed to change colors on.
I selected all the red objects in the card and did a color picker copy to the new red color.
After I did this it didn't copy to all of the selected objects. I thought it was annoying, so I did the quick test above to verify.
It always left one square as the previous color.