Bash Quoting Subshell Command Option With Equal Sign

Question

Why is this

function wtf()
{
  args="$*"
  set -o xtrace
  $(some_prog --option="$args") # note the '='
  set +o xtrace
}
$ wtf asd asd asd asd 
++ some_prog '--option=asd asd asd asd'

not the same as

function wtf2()
{
  args="$*"
  set -o xtrace
  $(some_prog --option "$args") # note no '='
  set +o xtrace
}
$ wtf2 asd asd asd asd
++ some_prog --option 'asd asd asd asd'

I believe I am running afoul of item #4 of Simple Command Expansion, but I'm not sure...

For reference, I want the behavior of the latter, to have $args be single-quoted. But I want to be able to use the equals sign, and I don't understand why the initial ' quote from $args is being propagated to the whole of --option=.