Why is this spline not right? Possible bug.

[Anonymous]

The two lower handles are colinear and  horizontal, yet I get that bulge.

[Anonymous]

Nothing? Seems pretty important.

[jeff_strater]

Actually, this is expected behavior.  I am not a math expert, but this has to do with the algorithm used in Fusion to fit a spline given the constraints of fit points and tangent handles.  Fusion splines are fairly "global" in the sense that changes in the spline can affect the entire curve.  For instance, in your example, if you drag a point or a handle away from the "flat area" you can see that this area is affected as well.  For instance:

start with this:

And move the blue highlighted point, we get this:

Again, I can't explain the math, but this is what I expect.

Jeff Strater (Fusion development)