Bug: func_reflective_glass reflects incorrectly sometimes

[ddddpplo]

Describe the bug

Sometimes when I look at func_reflective_glass it reflects perfectly fine, as a mirror should, but sometimes it seems to be reflecting from the completely wrong angle and position.

The angle where it works and the angle where it doesn't seems to be completely random. It depends on where I stand. The first screenshot shows it broken but the second one is fine.

EDIT: It somehow has something to do with the position of my portals. I think I'm seeing out the back the blue portal, not entirely sure.

Issue Map

It's occurring on a custom map I'm working on: https://www.dropbox.com/s/kuo1a71cdjgoybv/idk.bsp?dl=0

To Reproduce

1. Create a map with func_reflective_glass with any glass/reflectiveglass texture
2. Compile and run (placing cubemaps around the mirror doesn't help)

Operating System

Windows 10

[craftablescience]

Placing cubemaps doesn't affect this entity as the reflection is 100% real-time

[StefanH-AT]

How many reflective surfaces are in your map? Remember that only one planar reflection can be visible at once

[ddddpplo]

That's definitely what the issue was, I guess I didn't really know how realtime reflections like these worked when I posted the issue.