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?