Hi Valentin,
Thank you for your report. I have investigated this issue and I can confirm that this is a known side effect of using refraction. Unfortunately, because it is integral to the feature, this distortion is not something that we are planning on removing.
If Refraction is not producing the desired results for glass, a potential good alternative would be to use a Cubemap and translucent material. This would allow you to create a false reflection of the room and project it on the translucent windows. That would create the effect of glossy windows. Please let me know if there is anything else I can assist with.
Cheers,
Alexander