Hi again Dave... I think we've uncovered a 5.5.1 bug which is causing your problem.
See
https://www.ubbdev.com/threads/php/showthreaded.php?Cat=&Board=phpbugs&Number=44450I checked your board, confirmed that post numbers are getting "re-used" after getting deleted... then I tested over here, and noticed that the same thing was happening.
My boards, on 5.5 , don't re-use post numbers.
Max