>i understand that 'older' messages are not beeing (re)displayed. what i am talking about is i.e. the message i am replying too (yours) should have come up in the 'tree', it's a 'new' message', but it did not.

It didn't because at that time you were not subscribed to that forum.

>also, once i click 'send' when i finished composing this reply, this reply should appear in the 'tree', but i will not.

It won't if as per the above statement.