I just tested this and was unable to reproduce the problem. Have you tried refreshing the page and clicking the - button to the left of the Toodledo title on the Gmail sidebar?
As for the calendar sidebar, yes, that is expected with the instructions in that help topic that you referenced. If you want the Calendar sidebar, follow the directions at the bottom of this page: https://www.toodledo.com/widget/google_gadget.php
Jake, I'm having the same problem, too, but I can't tell you exactly when it started. I have the Toodledo gadgets in both my Gmail sidebar & my Calendar sidebar. Both show up but neither show anything in the task box itself, only the title bar. I'm using Firefox 23.0.1 as my primar browser & I also see it in Chrome Beta 30.0.1599.28 so it's not a specific browser issue. If you need more technical details to help fix this, let me know!
When I go into Gmail, I have to click the "..." icon at the bottom left of the screen to show the gadgets. Then I have to click on the "Toodledo" title bar to reveal the Toodledo gadget. This is how Gmail works.