quoting Torco:

my own posts always seem new to me

this is not a reflection on the freshness and style of my writing, nor on any putative lack of short-term memory on my part
rather, you know how the board highlights things in blue ? at least it does for me when they're new... it considers my own posts new until i've read them. is this a neat trick to entice people to see their posts again and realize what they're saying before anyone else does ?

It's more that your posts aren't treated any differently from anyone else's, so the site tells you that you haven't viewed them in the thread, which technically you haven't.