Go to the Oozie Workflow Editor of a particular workflow.
At the top right corner, below the blue header bar, there are several gray/black square shaped icons for Edit, Submit, Schedule, ...
Only the bottom half of these icons are active.
If you hover over the top half of any of these icons, the icon's look becomes normal (not the hover one), the tooltip disappears, and clicking doesn't work either. The latter one, not being able to click there was especially frustrating for me until I figured out it was the top half not working.
Expected: to be able to click anywhere on the icons.