The client dll uses a formula to select the proper portion of the .spr file based on the number it is trying to display. Since bytes can only go up to 255, when the Health message is received and stored as a byte, if it was actually over 255, then it gets stored as some crazy number. So when you put this into the formula, it starts grabbing strange coordinates for wacky places (such as the Half-Life logo this is displayed during the tram ride).
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No longer around. Thanks your support, everyone! As always: