Ok, where to start... By output panes I mean the windows "Search Results", "Usages", "Output" and so on, which are 
usually aligned at the bottom of the IDE window, and can contain several tabs each (so there's a two-level structure). 
There are a number of behavioral inconsistencies in that context, and also missing keyboard shortcuts for certain 
actions, both of which have been bugging me for some while. There is a certain overlap between the two, which is why 
I'm noting both in the same issue here.

The individual points are:

a) Keyboard navigation between panes and/or tabs: It is possible to navigate (= switch) between the panes with 
Ctrl+PageUp/PageDown, but only as long as the panes don't have multiple tabs. Once you've switched into a pane with 
multiple tabs, you are "stuck" in that pane, because then Ctrl+PageUp/PageDown now switches between the tabs within the 
pane. The only way to "get out" again with the keyboard is to select a different pane via the Window menu or via its 
specific shortcut (like Alt+Shift+U for Find Usages Results), assuming it has one.

b) There are no keyboard shortcuts for the "Close Tab" (or Close Pane, see point f), "Close All Tabs" and "Close Other 
Tabs" actions, and it also doesn't seem to be possible to assign any.

c) When there is only one tab, usually no tabstrip is shown, instead the tab's contents completely fills the pane. The 
only way to close the tab is to close the pane. No complaints here, but what is somewhat weird now is that "Close All 
Tabs" doesn't close the pane along with the tabs - an empty pane remains. There is no way to get to this state from 
when there is only a single tab. One reason this is relevant is that closing the pane can have a diferent behavior than 
closing the tabs, see issue 175620.

d) In "Search Results", unlike the other panes, a tabstrip _is_ shown even when there is only one tab. (This is 
probably for the information in the tab label to be visible. But compare with how Find Usages manages to do without.)

e) In Find Usages results, "Close All Tabs" actually does close the pane along with the tabs. So the behavior is not 
consistent across panes.

f) The behavior of Ctrl+F4 is inconsistent as well: In the "Output" pane it closes a single tab, while in "Usages" 
and "Search Results" it closes the whole pane.

g) While Ctrl+F4 closes a pane or a tab when it has focus, Shift+Ctrl+F4 still closes all editor windows.

So this is a bit of a mess currently, and also unfriendly to keyboard users.

My recommendations would be:

1) Never show the tabstrip when there is only one tab. (Make it such that the information on the tab label is only 
interesting when choosing between multiple tabs.)

2) Let "Close All Tabs" always be equivalent to closing the pane. (For issue 175620, this would probably have the 
implication that search results are not remembered anymore after closing the pane.)

3) Provide a complete and consistent set of keyboard shortcuts both for navigating through tabs and panes as well as 
for closing them.