System Information
Win7/64, AMD HD 6850

Blender Version
blender-2.70-be980b9-win64

Short description of error
see title

Exact steps for others to reproduce the error

1. Open
   RGBCurveUndo.blend52 KBDownload
2. Click on "Reset curve" in the RGB curve's tool popup menu.
3. Pressing Ctrl+Z doesn't do anything, but it should.
4. Display the undo history (Alt+Ctrl+Z here): There should be two items but there is only one. However, clicking on "original" undoes the action.

Another (minor) problem:
Open the file again, modify the RGB curve (by moving the point or something) and display the undo history: The action is labelled "Unknown action" instead of a speaking name. (but undo works)

Thank you!