I have two doc windows open, both in layout mode. On one window, I can use CTRL-3 to go to the 3rd tab of Inspector. In the other, none of the CTRL keys work but I can still use the mouse to switch tabs.
Nothing to do with having two windows. Standard menu set. Not consistent, as in it's been fine for the past hour but just started acting up and I couldn't say what I might have done to trigger such things.