Connected Galaxy Nexus to PC, and found that files were missing on PC File Explorer

Here's the odd situation I encountered:  I used FolderSync to sync between my android device and a Dropbox folder, which as the result sort of allows me to sync emulator .sav files between 2 android.  But that was not the main point.

The main point is that after a FolderSync session, there were some folders created on my Galaxy Nexus file structure, and I can actually see them when I use File Manager to view the files.  The problem comes when I hook up my Galaxy Nexus to a PC, and then from the PC File Explorer exploring the file system on my Galaxy Nexus, I DID NOT see those newly created files (and of course neither the files in those folders).

At the end, I solved the problem by rebooting the Galaxy Nexus, and found that after then all the files show up properly when hooking to a PC.  But still this is annoying, and I still don't understand what was going on.