Content opening in tabs doesn't save first time.

Here's what I'm doing. I need to edit each item in my collection. To make sure I get them all, I go to the edit screen and then open each item on the page in a new tab in Chrome.

When I save the first item, it works. But on saving subsequent items, I have to press Save TWICE in order to get it save. The page refreshes, but there's no "Content Updated" message, and when I check, the content wasn't saved. The change is still there on the screen.

I'm on Chrome 46.0.2490.71 (64-bit).

Here's my diagnostic report:

Perch Runway: 2.8.14, PHP: 5.6.10, MySQL: mysqlnd 5.0.11-dev - 20120503 - $Id: 3c688b6bbc30d36af3ac34fdd4b7b5b787fe5555 $, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (2.8.14), assets (2.8.14), categories (2.8.14), perch_blog (4.6), collection_5 (2.8.14), collection_2 (2.8.14), perch_forms (1.8.3), collection_1 (2.8.14), perch_comments (1.2), perch_members (1.3), perch_podcasts (1.1), perch_backup (1.2)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_comments', 'perch_blog', //'perch_events', 'perch_forms', 'perch_podcasts', 'perch_members', );
PERCH_LOGINPATH: /perch
PERCH_PATH: /PATH TO/local/perch
PERCH_CORE: /PATH TO/local/perch/core
PERCH_RESFILEPATH: /PATH TO/local/perch/resources
Image manipulation: GD
PHP limits: Max upload 32M, Max POST 32M, Memory: 128M, Total max file upload: 32M
Resource folder writeable: Yes
HTTP_HOST: local.capitalmass.org.uk
DOCUMENT_ROOT: /PATH TO/local
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

I guess this is to do with tokens to prevent the same form being submitted multiple times. Just wondered if there's a way round it?