This has been occurring frequently with other selection menus as well, but this is the most recent occurrence so I still remember how to recreate it.
- Open an actor asset from the [Content Browser]
- Create a primitive object within the actor
- Click the drop-down box under [Materials]
- Material description appears
- Attempt to apply a material by clicking through the material description
- Material selection dropdown menu will close as if cancelled or a material were properly selected
- Material will remain unchanged
Expected outcome: Material should change, regardless of having clicked the selection through the description window.
This outcome can become very frustrating, as the description window often follows the cursor. It was due to this bug that I had come to believe that only certain materials could be applied to certain object types, yet found no evidence to support this conclusion.