Funnily enough, many people didn't interpret Tedd as staying Tedd. Or, more accurately, they interpreted Tedd as genuinely morphing into a random person after having morphed into Diane.
I can see how they could have interpreted it that way, as I did change Tedd's figure and adjusted her figure a bit, but I would have changed the face (in particular, the eyes) more if that were the case, and I definitely would have made the hair noticeably lighter or darker.
Of course, anyone who's aware of the fact that I love to make awkward scenarios between Elliot and Tedd of this nature probably never even entertained the idea that Tedd could have possibly become anyone other than, well, Tedd after the brief Diane morph.