So wait. You're telling me that, even though I have PMs properly disabled, vBulletin allows anyone to PM me anyways and simply throws that PM away?!?!

Is that a correct understanding?

Yes, exactly. To me it looked like any other PM that was successfully sent.

Note that this is no different than an email sent into the ether; there's no guarantee it's been received or read.

Must be, I sent one a few months ago and thought it went through and was just ignored.

I don't even remember what it was about now. :/

It might still be in your Sent folder if you haven't cleaned it out.

Oh, going back to email:

Pedantic Pre-Response: responding to read receipt requests is a feature you can turn off in many email clients' options.