Shape hints misbehaving

[julia-ex]

I'm trying to have a trapezoid transform into a triangle. I want two points of the trapezoid to meet and the other two to stay anchored. I'm trying to use shape hints to achieve this but it isn't producing the result I want/expect. Any ideas about what's going wrong?

[kglad]

you need an intermediate tween.  probably just one will suffice.

[Mario_CR · Accepted solution]

Shape tweens can be unpredictable even with shape hints. This arrangement seems to work best for this particular shape, I do not know why though: 

[JoãoCésar]

Also, try to use as few points as possible so that shape tween will have a bigger chance to work correctly.