diversion while collecting arguments

I have a file with the following content:

define(show_arguments, `arg-1 = $1
arg-2 = $2
')

divert(1)A`'divert(0)a

show_arguments(
   divert(1)X`'divert(0)1st,
   divert(1)Y`'divert(0)2nd)

divert(1)B`'divert(0)b

- - - - -

m4 processes this file to:

a

arg-1 = X1st
arg-2 = Y2nd


b
AB

- - - - - -

I expected the
     divert(1)X`'divert(0)
and
     divert(1)Y`'divert(0)2nd)

to divert the X and Y so that it is emitted at the end.

Can someone explain why this is not the case?

Thanks

Rene