in Compose window, expander arrow doesn't remove all fields it adds

[Adam Dingle]

To see the problem:

1. Press New Message to open the Compose window. You'll see the fields To and Subject.
2. Click the expander triangle on the left. Two new fields (Copy and Blind Copy) will appear.
3. Click the expander triangle again. Only one field (Blind Copy) will vanish; Copy will remain.

This seems odd. I think that pressing the expander triangle twice should take me back to the original field set.

[Cris Dywan (kalikiana)]

Solved by literally doing what's needed: hiding the Copy field.