When certain subwindows/sidebars/dialogs are open, a single click anywhere else in the UI does not do the expected thing, which would be to open/view whatever you clicked on; Instead the first click just closes the current subwindow/dialog, and a SECOND click is required in the exact same place, to open the thing you clicked on.
This leads to much UI weirdness, such as:
After opening an entity view in the sidebar by Alt-clicking a reference-type cell in a Table View; now Alt-clicking a different reference cell in the Table View does NOT open that entity in the Sidebar; it simply closes the Sidebar (even though the hover hint over the cell says “ALT + Click” will open it). But regular-clicking on a cell WILL close the sidebar AND execute the click.
The same thing happens in the Apps and Templates page when a Type is currently being edited: clicking a different Type does not edit that type; it just closes the current entity’s definition in the right side of the screen.