**System Information**
Windows 7, nvidia quadro k5000
**Blender Version**
Broken: 2.71 RC2 a19c1be
Worked: 2.70a f93bc76
The material nodes in the node editor window won't undo when pressing the undo shortcut key(ctrl+z).
**Exact steps for others to reproduce the error**
Create a cube and add a Cycles emission shader and apply a gradient node to the color input. Change the gradient texture type from linear to quadratic in the node editor window then press cntrl + z to undo.