But help is at hand!
An updated firmware (albeit beta) gets it working.
Here's the link https://hc6800em.wordpress.com/2015/03/08/router-tl-mr3040-com-modem-vivo-huawei-e3272/ (choose the beta file from Option1: http://www.tplink.com/resources/software/_beta_TL-MR3040V2_140827_solve_WISP_can_t_connect_TrueWiFi_hotspoy_iPhone_isue.zip).
And here's how you update the firmware: http://www.tp-link.com/en/faq-688.html
Oh! And if you don't comprehend Portuguese, Google Translate is your friend :-)