Hmm, what were your steps where it worked?

Undo and other text editing facilities aren't completely nonfunctional, they just become broken and unpredictable. For example, these steps:

1. Load http://facebook.github.io/draft-js/ 2. Click in the text box 3. Type 'hello' on the keyboard 4. Using the mouse, choose Edit -> Undo

The text box will show "h" instead of being empty. Do you see this too?

Note that cmd-Z won't reproduce this since the page tries to handle that itself to work around these bugs.