Formatter not called

I have an Controller where i declare

jQuery.sap.require("ztest.model.formatter");

sap.ui.controller("ztest.App", {...}.

In Chrome i s that the formatter file is loaded an known.

In the associate View i have the following

<RadioButton id="DeleteYes" select="onReceiverTypeSelect"
selected="{path:'BuildingsModel>Yes', formatter:'formatter.getBoolean'}">
<customData> <core:CustomData key="Delete" value="Y"/> </customData> </RadioButton> <RadioButton id="DeleteNo" select="onReceiverTypeSelect"
selected="{path:'BuildingsModel>No', formatter:'formatter.getBoolean'}"> <customData> <core:CustomData key="Delete" value="N"/> </customData> </RadioButton> </buttons> </RadioButtonGroup>

The formatter is in both cases not executed.
Can someone give me an hint what is wrong here?

Regards

Dirk