It's the same as pressing either of the two arrow buttons on the tabs bar. It just takes you to either of the previous or next node you have visited (if you look at the left sidebar, it will be more obvious).
If you did a local search in a certain node and go back, then you will still get the search results from the node.
But if you did a global search, it moves you to "Search Results" node. So when you go back to the node later, you will always see the most recent global search results.
If you want to keep a certain global search results, move on to a new tab for a new search. When you switch back to the previous tab, it will show you the previous search results (but probably what's actually happening is it searches again and show the results).