2.0 - Observer Method not called when used in iron-list

[jogibear9988]

I've following component:

   Polymer({
        is: "mcc-image",
        properties: {
            imageName: { type: String, observer: '_loadimage' },
            language: String,

This component is used in a iron-list like this:

      <mcc-image image-name="[[item.Material.ImageName]]"

I've attached a breakpoint in the Method "_loadimage", but every time the method is hit, the value of this.imageName is undefined!

If I now select my "mcc-image" in chrome, and look via console $0.imageName, the image name is set, means my observer is not called.

This worked with the preview Version before!

[jogibear9988]

duplicate of #4601