I don't think it's a glitch. Basically every HL1 mod I've played, has this too. It's just coded into the engine. I think Valve figured that, when you die, it'd suck to get yet another death point if you want to change class. After all, your dying might have been because you're not good with the class you played as, and if you change class, you might have better luck next time. If you were punished with two death points, it'd be that much harder to keep up with the rest of the server.
Don't mind me though, just thinking aloud. :3