My application was stuck in a limbo like that for several months until I asked Suicizer about it on another site and he helped me out. My understanding is that it was a feature to prevent spambots that sometimes catches regular accounts.
Someone more knowledgeable hopefully has a better explanation.

Well, simply because there are a few dozens of spambot accounts per day that would completely ignore countermeasures and post crap without moderation, open registrations were put on lockdown and awaited approval by a human to determine legit ones. I had a note about that on the front page but it's missing now.

Clearly this can't go on forever, so i'm hoping there's some plans about the spambot problem so the registrations can be open again.