"Server" Field Not Shown in CURL -I command

Dear all, Using F5's command line, I have been trying to find out from the HTTP headers on what web server is serving out the web page.

Using curl -I and curl -v to get verbose response, the field "Server" was never shown. Other URLs did show the "Server" portion only a particular URL.

Anyone encountered this before or has knowledge on hiding certain HTTP header fields to show from CURL?