This is something that is encountered in small, refrigerating compressors. This winding is applied only in the auxiliary coils, even in the case of a sinusoidal windings.
Its purpose is to start the motor instead of the capacitor. If you're not very careful while recording the data, you're likely to make a mistake. Here is one example of such winding (internal diagram & and winding data).
More on 1phase sinusoidal you can find here.
Look for title: Part 1 of collection : "Single-Phase Sinusoidal windings" ( 24 slots, 2 pole; 13 diagrams)