Making dadoes

Attempting to make dadoes on A vertical component that has been opened for change. Using the rectangle tool to make the desired width and length. I click on the desired endpoint and drag to the desired length. But the ends of the dadoes have artifacts such as a blank partition. The internal part of the dado looks fine. On a non-vertical component the dadoes come out just fine. Am I selecting the wrong end point or edge? Any hints would be appreciated.

It would be very helpful if you share the .skp file so we can see exactly what you’ve got going on.