Unable to swap the names of two (new or existing) fields in Apps Within Minutes

While creating an application with "Apps Within Minutes", at the form creation page, if you try to add two date field on your form and verifying that identifiers of the two dates are different (say 'date1' and 'date' for example), clicking the "Next step" button leads to the display of a raw error message saying : "The class has two field that have the same name: date1".

If you try to get back to the previous page every modifications have been lost.

If you try to manually set different names on those date fields, this leads to the same error.