Forwarded an email with blank CC, but afterwards sometimes the CC is filled in

Hello,

I was using Maxthon web browser when this happened, and opened Gmail from browser, but this issue also appear in my Gmail app in Android. I don't think I was using any trigger setting or any Gmail add-on/extension.

Here's the story :

Part 1
I received email from my co-workers with me as one of the "To" recipients, and also there are other co-workers as "CC".

Part 2
I forwarded the email to my other co-workers (as "To") with some of my comments that is only meant for them. One of them was part of the CC from the first original email that I received (Part 1). I am very sure that I did not put any address in the CC in my forwarded email. So I forwarded it.

Part 3
When I was over hectic busy time, I looked back at my email. I clicked the "more details" part. And the CC was clean as supposedly. Nothing because I didn't put anyone in the CC. All is good.

Part 4
Just a few seconds or a minute passed by, I was shocked to see that the CC of my forwarded email (in the more details) suddenly filled with addresses from the CC of the original email (from the Part 1).

Part 5
If I close my message, open other message, or refresh my Gmail, I can see that the CC is blank again, but after sometime, in the more details, the CC suddenly filled with addresses from the CC of the original email (from the Part 1).


My question :
Was this just a glitch in "more-details" appearance? or I unintentionally CC-ed people?
I cannot ask to those people in the CC list whether they really received it or not, because it is supposed to be a confidential matter.

Can someone kindly please shed some light or confirm that I didn't CC-ed to people of my forwarded email?

Thank you in advance.

Johnny