I just checked and this is still a problem even in the master branch (i.e. TW and 15.1). When running the Partitioner standalone in an installed system, StorageManager#activate is not called (and there is no button to call it). We also need in the Partitioner something like this code from the installer: https://github.com/yast/yast-installation/blob/master/src/lib/installation/clients/inst_system_analysis.rb#L289