With the latest version of Postman Desktop App - I can no longer do a bulk edit of the request headers. Once I edit all the headers and click save, the headers disappear.
Editing in key-value mode works fine.
Hey @majumdarsohom 
Welcome to the Postman Community 
Thanks for reporting this - the team discovered the same problem this morning and are currently working on the fix.
I’ll update you once I know more information.