Unless I am really not understanding something with this block I have began to convince myself that something is wrong with it.
The block documentation seems to agree schematically with my first post/comment above but building up a simple model the block really does not behave in a way I am expecting it to.
I have a controllable AC source with a sine wave input. I have the primary side of the multi winding transformer set to 2 x 2 (2 on the left and 2 on the right) that is 2 on the secondary side also. Ignoring that the generated block symbol/mask is off I wire the two coils on the left in series and the two coils on the right in series. This should result in a 1:1 Voltage output. Similaraly if the primary is wired in parallel and the secondary in parallel this should result in a 1:1 Voltage
Please see model and scope results.

