I don't know if it has always been this way, but I just noticed some buggy behavior while playing around in my inventory. It will be a little difficult to explain, and it can't be captured in a screenshot, so bear with me.
So the expected inventory behavior goes something like this: If you click on an item, it expands and opens up the item details. While that item's details are expanded, if you click on another type of item, it will contract the previous item's details and immediately expand the second item's details. So in all normal cases, whatever item you click on should immediately expand its details.
This breaks if you click on the item you have expanded a second time. I noticed that when I click on the item I just expanded, it will contract the details as expected. However, this now leaves (for lack of implementation specific details) the state machine in a weird state. After contracting an item's details manually (through that second click), clicking on items behaves in a semi-unpredictable manner. Clicking on another item usually will still expand as usual, but once an item is expanded, clicking another item does not always do both steps mentioned in the previous paragraph. The behavior I saw most often, when clicking one item with another item expanded, was that the expanded item's details would just contract. The second item's details would not simultaneously expand, a second click is required to do so. I also noticed times where no item's details were expanded where I would click on an item and nothing would happen.
EDIT
Upon further experimentation, I've learned that this buggy behavior is not (only) triggered by manually collapsing an item's details, so it may not be related to that at all. I was able to reproduce the buggy behavior 100% of the time when I opened my inventory, filtered it to only look at my books, then I clicked each book to open it's details from top to bottom. I have six books, and opening the details top to bottom works fine. After I open the bottom book's details, I click on the book above it and the bottom book's details retract but the book I clicked on doesn't expand. If I then click on each book (starting with the book above the one I just clicked that failed to open), none of the clicks open anything. After doing that, it's hard to predict whether clicking on a book will or wont open its details.
It's worth mentioning, after further testing, if I open my inventory to my books and open them all bottom to top, the same issue happens after I've clicked them all once. Going back down the list only causes the top book's details to collapse and further clicks do nothing.
Refreshing the page gets it out of the buggy state, but I can regularly reproduce getting into the buggy state.
I am playing on Windows 7/Chrome/PC
EDIT EDIT
It is also worth mentioning this doesn't only happen with books. I experience the same thing with weapons (where I click through the list once then attempt to click back up the list and it fails), I imagine it would happen without any filter applied at all.