The mouse got somehow blocked during inventory operations - I could move the cursor around and use the scroll wheel, but clicking anything didn’t work. Keyboard still worked. Loading a different saved game didn’t help.
As a matter of interest, I remember the opposite happening to me a day or two ago: I could only use the mouse in the inventory/trade and the keyboard didn’t work. This never happened before 1.3, so I’m assuming that it’s a new bug.