You might also be using too few bounces - to pass through the glass and see what is on the other side. So you get black for the refracted rays. The appearance can be as though it's just a mirror. You really should show us what you're doing and seeing because your words simply tell us "it is glass" - nothing odd about anything you said.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)