johnbest ,
earlier it was not possible but now a member has the ability to delete his own posts which actually does create a lot of confusion , in market makers thread it was most common , many members want it to be disabled and even started a thread for this .
to avoid confusion best way is to quote him/her while replying .
yeah i too had same probleum on many occassions , i think it generally happens either with very old threads , most viewed threads or when too many members are at same thread 8-)