User registration reloading unless logged in at least once before,

I have this problem where some users, when trying to register and submitting the registration form, the form just reloads instead of submitting the info and showing the success page. The weird thing is that this only happens when no one has logged in into the site from that particular machine. Another strange thing is that verification for the form works fine, when a necessary field isn’t filled in the form reloads with the error messages.

I’m using Buddypress but to me it seems that this is more of a WordPress problem given the “logged in” situation when the form succeeds.

Any help is deeply appreciated! Thanks!