When you install Synaptic from Ubuntu repository, perhaps you'll find the Search Bar is missing on the toolbar. It's the same when you do it in another GNU/Linux distro that does not bring Synaptic preinstalled. The problem is because apt-xapian-index package is not installed and configured. Here is the solution.
Run these command lines:
sudo apt-get install apt-xapian-index
sudo update-apt-xapian-index --verbose --force
This picture shows what those commands doing:
There is no Search Bar. You must click the magnifier icon first then type the keyword.
The Search Bar is ready.
PS: I did this article on Trisquel 8 Alpha "Flidas".