Wow! It doesn't seem to be working for me either. I am using Internet Explorer 10, and experienced the following: (1) entered a new trackable, and the mission and description windows were grayed out, wouldn't take any input; (2) once the trackable was created and I clicked on the Edit This Trackable choice, the windows were still grayed out, would not take input; (3) tried to do the same with one of my existing trackables, and even though the listing showed data for both mission and description, when I clicked on the Edit This Trackable, nothing appeared in the two windows, and no input was possible.
I would be interested to know what finally worked for you. And when I tried the same thing with Chrome instead of IE 10, it worked normally. I'm not a big Chrome user, but maybe Groundspeak has left me no choice.
Okay, so here's my update. I can get it to work for IE 10 too, by simply turning on Compatibility View. That's funny, because Compatibility mode is meant to be used for websites "...designed for OLDER browsers...", for which Groundspeak said a few years ago they were "phasing oput support." But this indicates that Groundspeak isn't yet supporting or updating their code for the latest version/mods to IE 10, which I am using.