Not so.
I was out levelling a couple of days ago, received a tell from a spammer /blist add <r> them and continued on my way.
An hour later I was just killing mobs for quests and got another tell. From the same spammer. I know it was the same one as again I /blist add <r> them, but this time got "player already on blacklist". Reported it as a cheat and continued killing mobs again.
About 30 minutes later again I got a tell from that same spammer!

I've reported it in the bugs forum, but for some reason my topic was removed.
Added it to another thread in the bugs forum about a similar thing, and the topic was moved to the Duplicate Bugs forum.

I'll leave you to draw your own conclusions on that.