Talking about iMessages here. So when I get a message, while doing something already (basically: while the iPhone is not sleeping) a window will popup with the message and two buttons: reply and close (I think).
Now let's assume I do not want to reply right now, and I don't want to person to read it either (that's the point now). Obviously I won't click reply, instead I'd click close. But what "close" does is mark the message as read, and therefore the other person will know that I've read the message. It doesn't make any sense also because basically I've got two buttons which both mark it as read I'm not sure since when it does that, but it's annoying. Yes I could turn off read receipt, and no I won't do that because I want to keep it. So that when I read it for real - they know.
I'm not sure but I think if I click the button at the top of the iPhone, to put it in sleep mode, it will eventually not mark it as read. But, like I said earlier, this happens while I'm already doing something on the phone, and not while the phone is sleeping, so obviously I'd like to continue what I was doing, and not put the phone to sleep to wake it up again to avoid the person who sent me the message to see that I've read their message 
The iPhone thinks it's extremely smart and marks it as read only because the message was displayed and it believes I've read it. Why doesn't it do that when the message appears while the iPhone is sleeping, not so smart dear iPhone, huh?
Now let's assume I do not want to reply right now, and I don't want to person to read it either (that's the point now). Obviously I won't click reply, instead I'd click close. But what "close" does is mark the message as read, and therefore the other person will know that I've read the message. It doesn't make any sense also because basically I've got two buttons which both mark it as read I'm not sure since when it does that, but it's annoying. Yes I could turn off read receipt, and no I won't do that because I want to keep it. So that when I read it for real - they know.
The iPhone thinks it's extremely smart and marks it as read only because the message was displayed and it believes I've read it. Why doesn't it do that when the message appears while the iPhone is sleeping, not so smart dear iPhone, huh?