Sugar Module Builder not working

Hi,

since a while I try to use the module builder (starting with sugar 10.x, now sugar 11.x). But I simply fail.

As you can see in screenshots below I create a fresh module with a package.

Now I want to add a field. See screenshot:

But when I click on "Save" nothing happens. :( The field list is like in first screenshots. I tried it with various installations. various versions, various browsers within various operating systems. Always the same.

Can someone explain me, whats going wrong? Why this isn't working?