Question about whether clearing texts mark as read or leave unread?

Hey so if someone texts me and I don’t wanna respond yet I’ll clear the message and see it when I go into my messages to respond to later. I’m now on the Golden Master Build of iOS 12. Attached are screenshots and if I click clear I feel like sometimes it reads them (marking as read) and sometimes leaves them unread. I’d like to click the X and clear them but leave them unread. Can’t understand it or when it might do one thing or the other.

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