Comment 4 for bug 1447600

Same problem here. Basically I cannot install Kubuntu 15.04. Same symptom: installer hangs at 33% while preparing the ext4 file system. I currently have KUbuntu 14.10 and was trying to format the root partition and put 15.04 instead. Noticed that the installer didn't actually do any changes to that partition as was able to boot 14.10 without a hitch after my failed installation attempt. So apparently it doesn't write anything on selected root partition while being stuck at "33%".

Hope this helps and you fix it soon so we can all install 15.04.

Thank you.