Hey, I had this same problem and managed to fix it myself. If you go to /inc-cl/tr.php in the plugin directory and change line 334 from:
$postDate = (($options['useOrDate']=='1' && $post->post_date_gmt!='0000-00-00 00:00:00')?$post->post_date_gmt:gmdate("Y-m-d H:i:s", strtotime($post->post_date)))." GMT"; //## Adds date to Tumblr post. Thanks to Kenneth Lecky
to
$postDate = (($options['useOrDate']=='1' && $post->post_date_gmt!='0000-00-00 00:00:00')?$post->post_date_gmt:gmdate("Y-m-d H:i:s", strtotime()))." GMT"; //## Adds date to Tumblr post. Thanks to Kenneth Lecky
It should fix the problem. Use at your own risk – I don’t know if this fix affects any other functionality of the plugin.