Editable custom shape from Illustrator to Powerpoint

Hello everyone,

I'm creating an editable template for a client on PPT and my Illustrator custom shapes lose their transparency as soon as I modify the color...
In fact, PPT does not create a bounding box around the shape itself, but rather wraps it in a rectangle, thus adding color to the transparent areas as well. So annoying, does anybody have had the same issue before?

Thank you lots!