'Read ARFF' import operator does not pass data

I want to import a Weka file using the 'Read ARFF' operator. Its 'out' outlet is connected to the 'exa' socket of a 'Set Role' operator. Unfortunately, no data arrives that 'Set Role' operator, neither before nor after starting the process once (no matter which breakpoints).

The large "tooltip" box which appears on hovering the 'Read ARFF's 'out' output label, shows, *before* running the process:

Read ARFF.output (output)
Meta data: Data Table
Number of examples = 0
0 attributes:
Generated by: Read ARFF.output

After running the process, the box shows

Read ARFF.output (output)
Meta data: Data Table
Number of examples = 0
0 attributes:
Generated by: Read ARFF.output Data: Simple
ExampleSet: 150 examples, 5 regular attributes, no special attributes

So, after running the process, there are the 5 attributes acknowledged. Still, the table in the lower part of the box remains empty, and no example data or attributes arrive at the 'Set Role' op. If I set 'SetRole's 'name' parameter manually ('class' -> 'label'), it will say that the 'class' attribute does not exist.

It seems to me that I am doing it the intended way, and it works with the 'Retrieve Iris' op, but not with the 'Read ARFF' import.

Grateful for help.