When clicking on the CC Library dropdown within Photoshop CC, it snaps back to being in a closed state once I take my finger of the mouse button. It won't remain open in order to choose another library that I have in there.
You don't say which OS. It's working just fine on my Mac running Yosemite, and I don't recall a problem with it on my Mac running El Capitan. I can click on the drop down arrow and it stays open whatever else I do until I close it. I have it running docked in icon state, but I pulled it out and it still worked just the same.
I am having the exact same problem as Alex - the dropdown snaps back to closed when I release the mouse click. I have a large list of color libraries that extends the dropdown list past the size of the window, and the only way to fix it every time is to pull the window out and resize it which gets tiresome. I'm running Sierra on an early 2013 MBP. Please fix this soon!