kubuntu installer [Partman] crashed on partition create/format

the installer crashed after I had create a new Partition + format option. with follow Error-Msg:

Traceback (most recent call last):
  File "/usr/lib/ubiquity/ubiquity/frontend/kde_components/PartMan.py", line 453, in on_edit_clicked
    self.partman_edit_dialog(devpart, partition)
  File "/usr/lib/ubiquity/ubiquity/frontend/kde_components/PartMan.py", line 367, in partman_edit_dialog
    self.ctrlr.dbfilter.edit_partition(devpart, **edits)
  File "/usr/lib/ubiquity/plugins/ubi-partman.py", line 3286, in edit_partition
    assert self.current_question == 'partman/choose_partition'
AssertionError

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.6
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CasperVersion: 1.394
CurrentDesktop: KDE
Date: Fri Jan 4 10:47:49 2019
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/kubuntu.seed boot=casper maybe-ubiquity quiet splash ---
LiveMediaBuild: Kubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)