I use V-Ray defaults, so I don’t think that is the issue.
Why don’t you post a simple scene where it’s a problem and we can have fun figuring it out 
also only one of 4 glass presets in VRayMtl has Reflect on backside on.
It can’t be a reflection environment override issue since no reflection overrides are enabled in the default settings.
I’ll be sure to check that out. Thanks!
possible you need to lower the cutoff threshold for reflections/refractions? Reflect on backside is probably something that should be turned on if your glass geo has thickness. Not sure what would actually happen with a single pane of glass, if you actually get double reflections or not, but most newer house glass is usually double pane.
I toggled backface on, and it didn’t make a difference. I don’t have a single plan; it’s a box. I’ll play with the cutoff threshold for reflections/refractions and report back.
Did you try this?
Make a simple scene with a plane of glass and your HDRI and see what you see. Without a scene, we are all making wild guesses that are probably wasting everyone’s time.
In Bart’s simple scene you can see the environment relfected no problem.
You have a Dome light ? Or are you using HDRI in the environment? Do you have the environment overrides on in the render settings?
Just a little test. The red objects are inside the block the green are behind the camera.
Vray - Glass preset
My glass preset
The model is double pane glass. In my material preset reflections are actually set less than the glass preset of V-Ray, but my refractions are less and my IOR is at 1.55, also reflect on backside is on and a fog color with big depth.
But apart from that the preset still gives quite a bit of reflection so might be something wrong with either the model or some other settings.
And if you want even more clear reflections, like the example, just raise the IOR of the reflections. Done deal.
Also bonus tip: what I tend to do if I see there’s something wrong with the reflections in my glass, I just replace the material with a mirror material >to see if there’s something fishy going on behind the camera or with the settings. If that looks like it’s supposed to, it can only be the model or the material.
The first image seems to be correct, except for the sky: the luminous sky reflection mostly makes everything inside almost invisible. Now it seems as if the sky is not luminous at all!
Just a photo from Flickr:
In reality the dynamic range of in- and outside lighting is far more than with the usual lighting setup with any HDRI or Daylight setup.
To compensate for this I usually setup different output maps using the same VRaySky or HDRI to steer the environment, like Background, GI, Reflection and Refraction. Especially since clients often just want to see everything inside very clearly, which of course is unreallistic.
I use an HDRI in a skydome, and instance it in my environment, so I can see it in my viewport. I also have a V-Ray Sun, to boost my shadows.
So you don’t have anything in that highlighted override slot, then?
Or also a Dome light that could be blocking the view of the environment?
specular multiplier in dome light then.
It’s not very difficult to upload a stripped down scene but we can keep guessing ofcourse.
The problem is caused by Aliens? Or gnomes perhaps?