Setting coincidence for point on ellipse crashes Fusion 360

[r.moss]

This is a reproducible bug - after it happened twice in quick succession I did a screencast.  Since then it's happened twice more as I try to find ways around it.

I am trying to draw an ellipse to match measured dimensions on a plastic bucket (spoon) for a turbine.  I could not set these as driving dimensions (my first sketch attempt) because the sketch fails to solve.  So now I've started again (Sketch 2) with a simpler layout and I am trying to draw some construction lines.  The construction line that closes the triangle should run between the tangent points.  For some reason it didn't, so I then tried to make the points coincident.  This crashed F360.

PS.  You may spot that I didn't trim the left-hand construction line right back to the tangent point, as intended...I know!

[wmhazzard]

It's not clear to me what you want to do. 

Is this what you are trying to do?

[r.moss]

Oh dear, yet again the screencast hasn't uploaded to the forum.  This problem seems to have been around for years!  I tried selecting my screencast but then the web page said Invalid html so I attached a link to it instead, which doesn't seem to have worked either.

After about 15 attempts, I have managed to make a sketch that works.  I just have to be careful not to change some of the dimensions as I know it will crash - I must have seen 8-10 crashes today.  My original post was trying to make the blue selected line run between the two intersection points for the 30 degree construction lines and the ellipse.

I really wish there was some way of commenting sketch lines (a speech bubble or pop-up tooltip?) and/or colour coding them so that I can document the sketch and know which line is which when I come back to it in a few years' time.

It's an estimate of the cross-section through one half of a Pelton bucket.