Make remove multi and remove single work.

app/assets/javascripts/gl_dropdown.js.coffee

@@ -270,7 +270,6 @@ class GitLabDropdown
 
   rowClicked: (el) ->
     fieldName = @options.fieldName
-    field = @dropdown.parent().find("input[name='#{fieldName}']")
     selectedIndex = el.parent().index()
     if @renderedData
       selectedObject = @renderedData[selectedIndex]
@@ -278,10 +277,6 @@ class GitLabDropdown
     field = @dropdown.parent().find("input[name='#{fieldName}'][value='#{value}']")
 
     if el.hasClass(ACTIVE_CLASS)
-      console.log 'has ACTIVE_CLASS'
-      # if @options.multiSelect
-      #   console.log field.val(), value
-      # else
       field.remove()
     else
       fieldName = @options.fieldName
@@ -296,6 +291,7 @@ class GitLabDropdown
 
       if not @options.multiSelect
         @dropdown.find(".#{ACTIVE_CLASS}").removeClass ACTIVE_CLASS
+        @dropdown.parent().find("input[name='#{fieldName}']").remove()
 
       # Toggle active class for the tick mark
       el.toggleClass "is-active"
@@ -308,8 +304,6 @@ class GitLabDropdown
           # Create hidden input for form
           input = "<input type='hidden' name='#{fieldName}' value='#{value}' />"
           @dropdown.before input
-        else
-          console.log 'has field???'
 
   selectFirstRow: ->
     selector = '.dropdown-content li:first-child a'

app/assets/javascripts/labels_select.js.coffee

@@ -191,11 +191,13 @@ class @LabelsSelect
           else
             selected = $dropdown
               .closest('.selectbox')
-              .find('input[type="hidden"]')
-              .val()
+              .find("input[name='#{$dropdown.data('field-name')}']")
+              .map(->
+                @value
+              ).get()
             # need inline-block here instead of show, 
             # which will default to the element's style in this case inline.
-            selected = if selected? then selected.split(',') else ['']
+            selected = if selected.length then selected else ['']
             $loading
               .fadeIn()
             $.ajax(

app/views/shared/issuable/_sidebar.html.haml

@@ -87,9 +87,9 @@
               .light None
           .selectbox.hide-collapsed
             - issuable.labels.each do |label|
-              = f.hidden_field 'label_name', value: label.id, id: nil
+              = hidden_field_tag 'issue[label_names][]', label.id, id: nil
             .dropdown
-              %button.dropdown-menu-toggle.js-label-select.js-multiselect{type: "button", data: {toggle: "dropdown", field_name: "issue[label_name]", show_no: "true", show_any: "true", selected: issuable.label_names.join(","), project_id: (@project.id if @project), issue_update: namespace_project_issue_path(@project.namespace, @project, issuable.id, :json), labels: (namespace_project_labels_path(@project.namespace, @project, :json) if @project)}}
+              %button.dropdown-menu-toggle.js-label-select.js-multiselect{type: "button", data: {toggle: "dropdown", field_name: "issue[label_names][]", show_no: "true", show_any: "true", selected: issuable.label_names.join(","), project_id: (@project.id if @project), issue_update: namespace_project_issue_path(@project.namespace, @project, issuable.id, :json), labels: (namespace_project_labels_path(@project.namespace, @project, :json) if @project)}}
                 %span.dropdown-toggle-text
                   Label
                 = icon('chevron-down')