I found three matches and lit three candles, and where is the fourth match to light the fourth candle?

when does this game save im getting fed up of having to restart every time i log out

There are candles near small cubes in the corners of the room. When the candles are lit, it's clear that the light is supposed to shine through the cubes to create shadows on the wall, revealing special symbols. However, they only seem to appear temporarily. After a short time, they disappear, even though the candles are still lit. I managed to get one of them to reappear for a short time, but I have no idea how. Is this a bug?...