Distorted UTM polygons plotted over a geographic projection

[tonnirs]

I'm getting some weird distortions while using SAD69 datum to plot UTM Polygons, please take a look at the picture attached.

As you can notice there seems to be an "origin" at the middle of the plot that twists the polygons as they get further away.
I must use WKT as the method of input and the input measure is simply "FIRST(Geometry)" alike.
The "Size" field is set to 1 and the "Category" field is a unique identifier of the polygon.

The polygons are in UTM coordinates and I'm setting up the Proj4 CRS string as " +proj=utm +zone=22 +datum=SAD69 +units=m +south ".
Changing the zone to =44 seems to align the plot to the north, but the distortion remains.