I was just told by the systemd maintainers that this issue is fixed in systemd 251.
@Lauloque you never mentioned what OS you are running, but if its is Neon then I can say that the next Ubuntu LTS (coming out shortly) features systemd 255 - so when Neon rebases on top of that (should be around August through October, depending on which track you are following, if history is any indication) this issue will be finally resolved.
In the mean time - make sure the executable you are launching does not need escaping - possibly by creating a symlink with a simpler name and executing that.