Thanks for your report, that's not a bug. Free trial is given only ONCE per user per month. So if trial was removed, it means you or someone else used it from that IP.
As for FREE ones - they are free for life time without any payment. Could you please make sure that you are selecting the ones which label FREE? You can also send us email or open ticket, so we can better assist you. It looks like a bug in browser or the way you use tool... however, we will do our best to fix it in no time.