Trace bug?

We have discovered strange behaviour when tracing message sends. We turn on
tracing message send for a process. In R16 and 17 it seems like there is no
trace message when sending to a registered process name, while sending to a
pid generates a trace message as it should. In R15 however you get a trace
message both sending to a registered name and hen sending to a pid. Is this
a bug or is it a new undocumented feature?

As an example I include simple program in which worker sends a message to a
registered server and the server replies by sending the worker pid. Here
are outputs when running in 17:

Erlang/OTP 17 [erts-6.0] [source-07b8f44] [64-bit] [smp:4:4]
[async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Eshell V6.0  (abort with ^G)
1> c(trace_procs).
{ok,trace_procs}
2> trace_procs:start().
trace_procs 7 Server: '<0.39.0>'
trace_procs 10 Worker: '<0.40.0>'
trace_procs 34 Message: '{trace,<0.39.0>,send,answer,<0.40.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,answer,<0.40.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,answer,<0.40.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,answer,<0.40.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,answer,<0.40.0>}'

and in R15:

Erlang R15B03 (erts-5.9.3.1) [source] [64-bit] [smp:4:4] [async-threads:0]
[hipe] [kernel-poll:false]

Eshell V5.9.3.1  (abort with ^G)
1> c(trace_procs).
{ok,trace_procs}
2> trace_procs:start().
trace_procs 7 Server: '<0.38.0>'
trace_procs 10 Worker: '<0.39.0>'
trace_procs 34 Message: '{trace,<0.39.0>,send,{request,<0.39.0>},server}'
trace_procs 34 Message: '{trace,<0.38.0>,send,answer,<0.39.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,{request,<0.39.0>},server}'
trace_procs 34 Message: '{trace,<0.38.0>,send,answer,<0.39.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,{request,<0.39.0>},server}'
trace_procs 34 Message: '{trace,<0.38.0>,send,answer,<0.39.0>}'
trace_procs 34 Message: '{trace,<0.39.0>,send,{request,<0.39.0>},server}'

What gives?

Robert

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-module(trace_procs).

-export([start/0]).

start() ->
    Server = spawn_link(fun() -> server() end),
    io:format("~p ~p Server: '~p' ~n", [?MODULE, ?LINE, Server]),
    register(server, Server),
    Worker = spawn_link(fun() -> worker() end),
    io:format("~p ~p Worker: '~p' ~n", [?MODULE, ?LINE, Worker]),
    erlang:trace(Worker, true, [send]),
    erlang:trace(Server, true, [send]),
    trace_procs().

worker() ->
    timer:sleep(2000),
    %% whereis(server) ! {request, self()},
    server ! {request, self()},
    receive
        _Answer ->
            worker()
    end.

server() ->
    receive
        {request, Pid} ->
            Pid ! answer,
            server()
    end.

trace_procs() ->
    receive
        {trace, _Sender, send, _Data, _Recipient} = Message ->
            io:format("~p ~p Message: '~p' ~n", [?MODULE, ?LINE, Message]),
            trace_procs()
    end.