The helpUrl generated for UI components (by field name) works when it is starts with /descriptor or /descriptorByName (followed by class name of the describable and then /help). This is true when Hudson instance is the root of the Hudson web application. But it does not work in the cases where it is not the root. In this case, for the help to work normally, we need to have getHelpFile() returning a helpUrl starting with /descriptorByName.

The fix should be s/descriptor/descriptorByName in Descriptor.java.