I can confirm that the bug still exists. It exists in all my live-builds for jessie.
No problem to reproduce it with manual partioning. It happens every time I try to reformat and use an existing ext4-partions where another installation exists. In other words, a partition which holds a grub. If I erase the data on the partition first, then I'm fine. If not, it hangs indefinately on formatting that partition... Also, it's easy to reproduce in terminal... Without the force parameter, it hangs at this: (just pick a partition where you know there are another installation containing a grub) $ mke2fs -t ext4 /dev/sda6 mke2fs 1.42.12 (29-Aug-2014) /dev/sda6 contains a ext4 file system last mounted on / on Sat May 2 01:02:54 2015 Proceed anyway? (y,n) As you don't get to confirm this when using the Debian-Installer, it will hang forever at this point. Best, EW