There's an issue with some Roto shapes where adding a point to a shape that
has any animated Transform curves will cause Nuke to set shape keys on
every frame in the current script range.
To reproduce:
1) Create a Tracker, add a track, and track something for a few frames.
2) Set the Tracker node's transform mode to "match-move."
3) Create a Roto node and add a simple shape.
4) Select the shape, go to the Transform tab of the Roto node, and copy the
animation from the Tracker's 'translate' knob to the Roto shape's
'translate' knob (using Shift + drag).
5) Close the Tracker control panel, go back to the Roto tab on the Roto
node, and then add a point to the selected roto shape.
At this point, if you open the Dope Sheet or look in the Viewer timeline,
you will see that Nuke has created keys for the shape at every frame in
your script.