Converting qcow2 to vmdk on MacOSX results in a non-bootable image

When using qemu-img convert -O vmdk  with version 3.1.0 or 4.0.0 on OSX (10.14.3) with a qcow2 image  (https://cloud-images.ubuntu.com/bionic/20190703/bionic-server-cloudimg-amd64.img), the resulting image is not bootable.

Running the same command on Ubuntu 18.04 results in a bootable image as expected