This occurs when you've turned the entire object (all four rail brushes) into one entity.
To be able to see the other rail at the opposite side of the room while looking though it from the other side, you have to turn each rail brush into it's own entity.
In your case, you have four rail brushes, one on each side of the green liquid container. Turn each individual rail brush into the entity of your choice (func_illusionary) and the problem should be fixed.
But yes, should use OpenGL mode, not Software mode.