Connect to a FTP server using IPv6?
ICS has IPv6 support, but only on mobile data networks; it's somewhere between buggy and nonfunctional on Wi-Fi.

Issue 3389 lists a wide variety of Android IPv6 bugs. Your issue is probably among them.

I've been using IPv6 successfully on my Verizon Droid RAZR MAXX since I got it almost a year ago, on ICS. Works great on 4G LTE. No idea what Jelly Bean does on Wi-Fi since I haven't gotten around to redoing my home network to bring IPv6 into every subnet yet...when I do, I'll be sure to update this.