Running multiple show commands with `+` isn't working

[lefou]

Reproducer:

> mill init javalib/basic/3-multi-module
No mill version specified.
You should provide a version via a '//| mill-version: ' comment or a '.mill-version' file.
Using mill version 1.0.5
[build.mill-59/64] compile
[build.mill-59] [info] compiling 3 Scala sources to /tmp/mill1/out/mill-build/compile.dest/classes ...
[build.mill-59] [info] done compiling
[1/1] init
[1] Downloading example from https://repo1.maven.org/maven2/com/lihaoyi/mill-dist/1.0.5/mill-dist-1.0.5-example-javalib-basic-3-multi-module.zip...
[1] Unpacking example...
[1] bar
[1] bar/test
[1] bar/test/src
[1] bar/test/src/bar
[1] bar/test/src/bar/BarTests.java
[1] bar/src
[1] bar/src/bar
[1] bar/src/bar/Bar.java
[1] build.mill
[1] mill.bat
[1] foo
[1] foo/src
[1] foo/src/foo
[1] foo/src/foo/Foo.java
[1] mill
[1] Example download and unpacked to [/tmp/mill1]; See `build.mill` for an explanation of this example and instructions on how to use it
[1/1] ============================== init javalib/basic/3-multi-module ============================== 10s

> mill show foo.jar + show bar.jar
[build.mill-59/64] compile
[build.mill-59] [info] compiling 1 Scala source to /tmp/mill1/out/mill-build/compile.dest/classes ...
[build.mill-59] [info] done compiling
[1/1] show
[1-69/79] bar.compile
[1-69] [info] compiling 1 Java source to /tmp/mill1/out/bar/compile.dest/classes ...
[1-69] [info] done compiling
[1-72/79] foo.compile
[1-72] [info] compiling 1 Java source to /tmp/mill1/out/foo/compile.dest/classes ...
[1-72] [info] done compiling
"ref:v0:b0782d30:/tmp/mill1/out/foo/jar.dest/out.jar"
[1/1] ============================== show foo.jar + show bar.jar ============================== 6s

> cat out/{foo,bar}/jar.json 
{
    "value": "ref:v0:b0782d30:/tmp/mill1/out/foo/jar.dest/out.jar",
    "valueHash": -479423802,
    "inputsHash": -806575525
}cat: out/bar/jar.json: Datei oder Verzeichnis nicht gefunden

Observation:

• There is no out/bar/bar.json and out/bar/jar.dest/out.jar
• There is no show output for the result of bar.jar

Expectation:

• Both jars out/foo/jar.dest/out.jar and out/bar/jar.dest/out.jar are created
• The output shows both result jsons

[lefou]

As a workaround, one can use

> mill show foo.jar \\+ bar.jar
[1/1] show
{
  "foo.jar": "ref:v0:b0782d30:/tmp/mill1/out/foo/jar.dest/out.jar",
  "bar.jar": "ref:v0:e695f764:/tmp/mill1/out/bar/jar.dest/out.jar"
}
[1/1] ============================== show foo.jar \+ bar.jar ==============================