Property field has 2 forms to enter properties. How to use?

First off, great module and thank you so much for your effort.

Second, I'm puzzled (don't worry I often am :P):

Some field types of the type "long text" and widget " multiple rows" offer the user more than one opportunity to input properties.

Please see the attached screen shot.

Oddly enough not all field offer two input forms, even though the field type and widget are the same.

Question 1: Under which conditions am I presented with this setup?
Question 2: How should I use these two fields?