Corona is physically based as much as possible and fakes are not always welcome.
The issue here is that receive shadow parameter also conflicts with reflections, as you cannot clearly distinct what is shadow and what is a reflection from/in that shadow.
Try disabling visible to reflection/refraction as well, see if it brings any improvement.
But workaround(s) has been available for quite some time.
You can use rayswitch material with no GI slot to "disable" that object from light calculation, which will also disable the shadows cast from/by it.