Incorrect representation of data

[nafem]

If I use the following data set, I would expect two circles with an overlap in the middle with one item in:

[ {"set":["A"],"name":"node_1"}, {"set":["A"],"name":"node_3"}, {"set":["A"],"name":"node_4"}, {"set":["B"],"name":"node_2"}, {"set":["A","B"],"name":"node_6"}, ]

But instead I get

Is the data incorrect or is that how the plugin is intended to work?