Multi Term: source field can not be added when hieraichally linked to a certain category

Dear all, I have encountered the following Problem in MultiTerm 2014 and 2015 Desktop and I hope you can help me out. I have created a termbase with Definition and Definition source. The source is hierarchically linked to the definition field. When adding an entry I can fill in the definition but when clicking the arrow to add a definition source, the field doesn't appear. The same happens with context and context source. What goes wrong? If this question has already been asked and answered, please bear with me and provide me the link to this entry. Best regards Anja