Output PNGs from PI Render are squashed

Hi there,

I have a problem with particle Illusion Render:
I tried to render PNGs of an Effect in Full HD (1080x1920) and the PNGs are squashed in width.
The strange thing is, if I open them in Windows Picture Viewer, they pop up at the correct aspect ratio for half a second and then squash to square shape.When I import them into After Effects, they are also squashed.
I tried the same with a custom aspect ratio like 1500x1200, but that also resulted in squashed PNGs.

Is there any setting or workaround to avoid this or is it a bug?

Kind regards,
Marco Rosenberg