ok that mysterious "dissapperance" of post happened to me again.
I added one reply in the thread of "Leut Kuttiyah"(2010) in the lakorn section, and after I clicked "Post", the webpage redirected to the home page of Spicy, instead of the thread's page. And I checked that thread, found out that my reply dissappeared. I redo the same procedure, and this time it was successful.