Issue with skin property and String.Compare

I use a python service to populate some properties in the skin. In the python service i use WINDOW.setProperty("service.Test1","off") I have set the window id to 10000.

In the skin i'm able to show the content in a label with $INFO[Window(Home).Property(service.Test1)]

Now i want to show a picture if the content is set to on.

So i have tested with <visible>String.IsEqual($INFO[Window(Home).Property(service.Test1)],on)</visible>
This is not working. I have tested with Substring also. It seems String.IsEqual is always False.

Do oyu have any idea why or do you know another solution?