FIX: only remove custom CSS in admin on first load

app/assets/javascripts/admin/views/admin.js.es6

@@ -1,6 +1,9 @@
 export default Discourse.View.extend({
   _disableCustomStylesheets: function() {
+    if (this.session.get("disableCustomCSS")) {
       $("link.custom-css").attr("rel", "");
+      this.session.set("disableCustomCSS", false);
+    }
   }.on("willInsertElement"),
 
   _enableCustomStylesheets: function() {

app/helpers/application_helper.rb

@@ -153,11 +153,14 @@ module ApplicationHelper
     MobileDetection.mobile_device?(request.user_agent)
   end
 
-
   def customization_disabled?
     session[:disable_customization]
   end
 
+  def loading_admin?
+    controller.class.name.split("::").first == "Admin"
+  end
+
   def category_badge(category, opts=nil)
     CategoryBadge.html_for(category, opts).html_safe
   end

app/views/common/_discourse_javascript.html.erb

@@ -9,7 +9,6 @@
 
 <script>
   Ember.RSVP.configure('onerror', function(e) {
-
     // Ignore TransitionAborted exceptions that bubble up
     if (e && e.message === "TransitionAborted") { return; }
 
@@ -43,6 +42,7 @@
   Discourse.Route.mapRoutes();
   Discourse.start();
   Discourse.set('assetVersion','<%= Discourse.assets_digest %>');
+  Discourse.Session.currentProp("disableCustomCSS", <%= loading_admin? %>);
 </script>
 
 <%= script 'browser-update' %>