If you create a parameter for a material node's material field. Then save. The user interface works as expected.

If you return to the type properties and change the label for that same parameter. Then apply, then accept. You will notice that the material node has lost its channel expression but is still green in color indicating it has a channel.

This seems like a bug to me. File attached.

Houdini Apprentice HD 10 running on Vista Premium i7 920.