Yes, this, and also what nightsky wrote - people are often different in writing (including email even though it is closer to speech than many forms of writing). This is the one thing in the world that I can say with confidence that I know something about - I spent several years of my life doing research on it. So don't interpret a cold-seeming email to mean that your T has turned cold. But if it is a problem, I think it's a good idea to bring it up with them.