strange double reflections whith glas ! Is this normal ?

[stereoV]

Hi Guys,
i get these strange double reflections with refractive materials like glas, when i decrease the glossiness value in the reflection channel below 1 p.e. to 0,99 or if i load in a texture which is not absolutely white, some noise p.e. . The thinner the object the stronger the effect gets !
Is that right in corona for c4d or is this a bug ? Some friend told me in corona for max it´s not like that !
I never saw this behavior in reality, so please see the example pics or check my testscene for a better understanding !
Looking forward to your responds...
THX and cheers guys

[TomG]

It's the reflection off the back face, and does happen in Max too, and in the real world (see https://sc01.alicdn.com/kf/HTB1pw32JXXXXXbGXFXXq6xXFXXXv/special-design-3d-laser-engraving-crystal-solid.jpg_350x350.jpg as a randomly googled example)

The double reflection is there even with Glossiness of 1. It is true though that lowering the glossiness from 1 causes a much greater separation between the reflections - I don't know the calculations behind all that to say if that is correct and expected, so that would be down to the devs there.

Attaching two grabs from Max, with glossiness of 1 and 0.999

[stereoV]

Thanks Tom for your quick reply !
Yeah that seems plausible what you wrote and i wouldn´t get a problem if the double reflection had a distance of 5mm on a 5mm thick glas pane like with value of 1. But that distance changes with values below 1 is strange !? Even more strange is if you increase the thickness of the object it decreases the distance of the reflection ???