Hi Saskia,
Thanks for reporting this problem! We reproduced it on our end and will do further research to figure it out. We will keep you posted about the progress.
Please work around this issue by using editmask.mask instead of edit.format, for example:
dw_2.object.c_date.format = ls_format
dw_2.object.c_datetime.format = ls_format
dw_2.object.c_date.editmask.mask = ls_format
dw_2.object.c_datetime.editmask.mask = ls_format
Regards,
Appeon Support Team