Hi Tamas,
Please check the structure CI_EEW_BUT000 and see if the field has been included/appended. If it is not, create an append structure to add the field. After activating the structure, the field should be visible in the Web Dynpro field Repository. The structure CI_EEW_BUT000_X should also be appended with the field.
Edit: You shouldn't have to, but just in case you might want to regenerate the BP structures after this.
Hope this helps.
Thanks,