Do we have to change the way we say hello in private messages?

Every now and then I’ve gotten the feeling that some messages get lost on their way to the user they were sent to. I think I’ve figured out what’s going on: if you’ve posted the exact same comment before (say, “Hey there!”), the system assumes you’re accidentally posting it again, even if you posted it days or even weeks ago, so it doesn’t get delivered. Am I right? If so, could it be fixed?

I just checked and the same happens with answers on questions. But then, I guess it makes more sense there (and it’s easier to notice if you’ve posted the same answer before).