Cookie left by Design bookmarklet causes "There is a validation error with your HTML input. Your activity is a bit suspicious, hence aborting"

I use this bookmarklet when I develop sites. http://sprymedia.co.uk/article/Design. It leaves cookies for the site's domain named SpryMediaUK_Design, SpryMediaUK_Grid and possibly others.

After upgrading to CiviCRM 3.3.2, I was unable to hit any /civicrm page without getting this error:

Sorry. A non-recoverable error has occurred.
There is a validation error with your HTML input. Your activity is a bit suspicious, hence aborting
Return to home page.

Backtrace is:

/var/www/staging/sites/all/modules/civicrm/CRM/Core/Error.php, backtrace, 270
/var/www/staging/sites/all/modules/civicrm/CRM/Core/IDS.php, fatal, 231
/var/www/staging/sites/all/modules/civicrm/CRM/Core/IDS.php, kick, 165
/var/www/staging/sites/all/modules/civicrm/CRM/Core/IDS.php, react, 144
/var/www/staging/sites/all/modules/civicrm/CRM/Core/Invoke.php, check, 88
/var/www/staging/sites/all/modules/civicrm/drupal/civicrm.module, invoke, 356
, civicrm_invoke,
/var/www/staging/includes/menu.inc, call_user_func_array, 348
/var/www/staging/index.php, menu_execute_active_handler, 18

The error log is attached.

Deleting the cookies will let CiviCRM operate normally.