I'm using the perimeter circle sketch tool, and my circle seems not to be interested in staying on the points I'm drawing it on. Is this a bug, or am I doing something wrong? Sometimes it works, then breaks when I try to add another shape or line to the sketch. I've attached a simple example where I drew two lines, then a perimeter circle defined by the 3 points defining the lines. For some reason the circle does not want to sit on the points I've drawn it on. The second attachment is a successful example. It seems like the error is less likely to happen if I fully define the lines first.

I am not getting that error. Even in the first file where the lengths of the lines are not dimensioned, if I draw a perimeter circle selecting the line endpoints and the origin then the circle stays constrained to those points. Of course the circle can still move around because the ends of the lines are not constrained, but however I move it it still stays coincident to the line ends and the origin.

I just realized what is happening. You have to be careful when you are selecting the points because if you move the mouse over one of the lines in a certain way then it suddenly wants to add a coincident

anda tangent mate. When that happens it's weird because it will still let you select the third point, but when you do I guess it doesn't add the coincident mate. So just make sure it isn't adding the tangent mate as shown below. Selecting the points in a different order might help.