New message visibility

Hi all,

lately I've had quite a few messages I sent appear unopened, even though the recipient has been active since I sent them.

I don't get many messages myself so can't tell, but is it possible that as messages are goruped by thread, messages are pushed further down the list by newer messages in another thread and the recepient would have to scroll down to see them?

I just don't get it - I'm prepared to accept people don't want to reply *after* they opened my message, but to not open them at all seems strange...