Description of problem:
Hovering over the button should tell you what it does.
When a bug is in the right state and the "Start Working" button is shown, then it has pop-up text when you hover over it.
This bug has been resolved in Red Hat Bugzilla 5 and can be tested on https://beta-bugzilla.redhat.com
If there are any issues, do not reopen this bug. Instead, you should create a new bug and reference this bug.