The problem is that the parameters passed to the function used with "Wait for signal" and "Signal" ain't stored. So the when you call the function the first "Longtext" reads the parameter (1) then it waits for a signal, but as it does this the parameters for some reason is "cleared". If you replace the "Set text to function.Param(2)" with for instant "Set text to "test text 2"" then it will work.
It seems that it might be a bug as im not sure its suppose to work like that, so you can take your chances and make a bug report, but personally if I were you, I would just start creating a workaround for what you are trying to do, because it will most likely not be the last, so you might as well get used to it