When you press Ctrl-F to open "Find" within document a toolbar is opened at the bottom of the document that allows you to enter the word(s) that you want to search for. If you select the drop down menu for this tool bar and select "close toolbar" the Find tool interface disappears, but the tool bar stays open. To get the toolbar to fully close you must deselect the "View -> Status Bar." On small screen the lost of screen real state by not closing properly is annoying.
The 'Esc' button ['Escape'] is the right shortcut key to close the complete 'Find toolbar'. See: http://artax.karlin.mff.cuni.cz/~kendy/blog/archives/monthly/2011-03.html#2011-03-04T10_18_40.htm
I've had this issue as well, and would love to see a "fix." The tip to hit ESC as an alternative to mouse-closing the toolbar is helpful. But I still see it as a glitch that an empty toolbar stays open.
*** This bug has been marked as a duplicate of bug 36475 ***