ListModel.sync() leaves one model object hanging

Insert item to ListModel just before refeshing the model in WorkerScript.

Expected result: After sync the changes in worker thread are synced with the main thread.

Actual result: One model data object with undefined roles is left hanging around.

See attached code example, where the model is refreshed with WorkedScript after 5 second Timer timeout. GridView shows ten items even though ListModel count is 9.