Here are some explanations and workarounds that may be helpful:
1) Place some of the splines on another layer.
The problem seems to be caused by having many splines on one layer.
2) Use smoothed polygons and freehand shapes in lieu of splines.
3) If layer is corrupt try these techniques to recover as much information as possible:
1.Select objects on that layer with the mouse, by dragging a rectangle around them. Do not use the Select All command, as this will not remove the corruption.
2.Use the Cut command to remove the selected objects.
3.Past the objects onto a new layer or into a different document.
4. Delete the damaged layer.
The file should work properly after these steps.
Note: This was resolved in Claris CAD 1.0 v5