Pass the required parameters on search submit.

app/views/projects/issues/_head.html.haml

@@ -20,6 +20,11 @@
         = form_tag project_issues_path(@project), method: :get, id: "issue_search_form", class: 'pull-left issue-search-form'  do
           .append-right-10.hidden-xs.hidden-sm
             = search_field_tag :issue_search, nil, { placeholder: 'Filter by title or description', class: 'form-control issue_search search-text-input input-mn-300' }
+            = hidden_field_tag :state, params['state']
+            = hidden_field_tag :scope, params['scope']
+            = hidden_field_tag :assignee_id, params['assignee_id']
+            = hidden_field_tag :milestone_id, params['milestone_id']
+            = hidden_field_tag :label_id, params['label_id']
         - if can? current_user, :write_issue, @project
           = link_to new_project_issue_path(@project, issue: { assignee_id: params[:assignee_id], milestone_id: params[:milestone_id]}), class: "btn btn-new pull-left", title: "New Issue", id: "new_issue_link" do
             %i.icon-plus