Found this interesting phenomenon on 'c1a0' map (first map after the train ride) while running in software rendering mode. As far as I explored the map, the artifact occurs only once for the level on this cabinet. This most likely happen because of the incorrect UV texture coordinates interpolation through the triangles. I don't really think that such assumption in texture mapping accuracy was made to speed up the game, then it would also make sense to optimize not only this one object on the en…
Half-Life definitely has some interesting spots that have 'smooth flowing' from one atmosphere to another. When you play the game, you might not notice such changes in tones. For that time it was impressive, I think.