It's impossible to search in the file chooser if a query contains several words. When you press the space, you activate the first search result: if it's a directory, you move to the corresponding location, if it's a file, it's opened. This happens because the focus is constantly moved from the search field to the search results list as you type. This was reported here: https://bugzilla.gnome.org/show_bug.cgi?id=767736