I didn't realize I'd done this until I looked around the UI a bit...
I selected an item within my inventory, which opens the action menu for that item. Then (distracted, apparently), I clicked on the quest notification icon up by Pet Rock. I tried to click the link to learn more about the quest, and it took me a few minutes to realize why it wasn't opening.
The action menu for the item in my inventory was still open. Once I clicked "never mind," I was able to open the learn more link just fine.
Might not necessarily be a bug, but could cause some confusion.