interior mode refraction behaving strange

[zooropa]

HI.
My refractions are behaving different in Interior Mode vs Product mode.
I would like to use interior mode (I find it more realistic). The wood under the acrylic volume looks different when I activate interior and caustics ( I can not do it without caustics in interior mode). They show some grey edge.

Please find the comparison between interior and product mode.


If you have any tip regarding transparent surfaces and lighting I would appreciate some insight.s