Hi,
It sems that the website is tracking your mouse movement on the button (may be to learn your shopping behavior/how you decide to buy things,...). When It sees change on the text, it will add the original text again. The extension will see that change and apply styling to the new text. This procedure will keep repeating again and again. As a result, you will see "buttonbuttonbutton"....

Unfortunately, whenever I visit "overstock.com", I always get error: "An appropriate representation of the requested resource / could not be found on this server". For that reason, I couldn't make further investigation on that page.

As for now, you can try the following:
- Add "overstock.com" to blacklist.
- Use keyboard shortcuts to disable/enable the extension.
- Turn off ALL button and use Ctrl+Alt+B to manually enable styling for a webpage.