EVA construction on surface vessels makes them fall when you click on a supporting part (leg, wheel, etc)
In the clip below from when I was playing on Twitch, clicking a landing leg of the lander while in EVA construction mode immediately made the lander fall over. This is because it assumes when you use rotate tool or move tool on a part, that you are removing the part from the vessel, so it acts like the landing leg is no longer there, causing it to tip over the instant you click the part. I have had the same issue with trying to straighten the rover wheels on the new "repair rover" contracts - because the wheel is temporarily "not there", it makes the rover fall over while you're trying to adjust the part so it moves and tumbles down a hill.
(There is also a clickthrough bug on the inventory window that caused the click on the landing leg in the first place in the clip here, but that's a separate issue I made a moment ago. THIS issue is about how any click on a supporting part resting on the ground makes the vessel fall over because it treats Move and Rotate as if they were removing the part, making repairing rover contracts a real pain.)
Please forgive the yell in the video clip - this happened while I was playing live and I didn't understand what was happening until I thought it through later and made this bug report.