I'm doing the Table Wizard tutorial and ran into the problem that I was in another tab because I just couldn't zoom deep enough and then couldn't add the ancestor reference. This is close to being a bug, though I was able to get as deep as I could in one window and started hitting the expand button until I was able to right-click in my target action and add the ancestor reference. Things were getting pretty small by the time I did that, though.
Using Tersus Studio 188.8.131.52 on Mac.
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