Why isn't Finder updating a folder's contents? Today I had the strange behavior that I added some files to a folder in Finder (that happens to be in dropbox) from Outlook, but Finder did not show them.  I could see them from the Open File dialog of Outlook and of Adobe Acrobat Pro XI, but returning to Finder, still not there.  Hitting the F5 key to force a refresh, still nothing.  Finally, I forced Finder to quit and relaunch, and they showed up.  This is OS X Yosemite v10.10.2.

What is going on?  Why would Finder not show the new files until forced to restart?
I've known it happen if memory was being paged heavily, or if a drive was particularly full. 

F5 has no effect on a Mac, btw, it's a Windows command.

The only real equivalent - to a system that really ought to never need to be refreshed under normal circumstances - is to switch view style…

…from list to column then back again, for instance…
 Cmd ⌘   3  then  Cmd ⌘   2