Spline handles are "invisible" when created through animate editing mode

There may be more ways to reproduce this, but I’ll just go off of what I did:

  • Create a looped spline on frame 0.
  • Enter animate editing mode.
  • Jump to a later frame. In my case it was frame 60.
  • Move the vertices and tangents around.
  • Add some vertices by right-clicking the spline and selecting “Insert Item & Keep Shape”.
  • Move the vertices and tangents some more. (Probably not a necessary step.)

Now play the animation. Prior to the frame you added them, the spline handles are “invisible” and cannot be changed by the user.

What’s especially strange about this bug is that the spline outline and fill region don’t agree with each other at all. Synfig knows the vertices are supposed to be there, uses them to fill in the region, and offers them in the parameters window, but their handles aren’t available and they aren’t used to draw the outline.

Is this a known bug? Or is it a “feature”? Are there any workarounds, or am I going to have to create the spline on the frame when I have the most vertices?

Here are some pictures of what I’m referring to:
Frame 0. There are just four vertices.

Frame 60. I’ve added three vertices.

Frame 59. Now the added vertices’ handles are invisible and can’t be manipulated. They still show up in the parameters window and, bafflingly, are used to generate the fill but not used to generate the outline.

It is a feature. If you create vertices in animation mode they grow from 0 to 100 visible in an interpolated way from the previous keyframe to the time you created it.
It has some bugs reported because the behavior it not completely what it should be as we the users would like it to be. It was coded like it works for you from the very first version of Synfig.