When composing a new email message, if:
You have Settings -> Mail -> Compose -> “Show CC and BCC fields when composing” UNchecked
And you click the “To” button on the New Message
And highlight a Contact in the Select Contact box
And click the “CC:” button
And click the “OK” button
…then back in the New Mail message form, that CC (or CCs, or BCCs) will not be shown, unless you then click the “Add Cc & Bcc” button.
I’d consider that a bug, because it looks as if you haven’t added any CC recipients (especially if you also added some “To” recipients). My suggestion is that if you add a CC or a BCC in the Select Contact box, then when you return to the New Mail form (by pressing “OK”), that form should then automatically show the CC and BCC fields, as if you had clicked the “Add Cc & Bcc” button. (And, of course, that button’s text should also be changed to “Add CC & BCC”.)
This report is relevant to version 5.0.17595.