gulp task starts but does not end - gulp

Question

I have the next files structure:
src/
themes/
default/
1.png
2.png
oneMoreTheme/
3.png
4.png
dist
themes/
default/
oneMoreTheme/
and the next gulpfile:
'use strict';
var gulp = require('gulp'),
_ = require('lodash'),
plugins = require('gulp-load-plugins')();
gulp.task('images', function () {
var streams = {},
themes = [
'default',
'oneMoreTheme'
];
streams.themesImages = [];
_.forEach(themes, function(theme) {
streams.themesImages.push(gulp.src('src/themes/' + theme + '/*.*')
.pipe(gulp.dest('dist/themes/' + theme + '/')));
});
streams.allThemeImages = plugins.merge(streams.themesImages);
return streams.allThemeImages;
});
I can not understand two things:
1) Why do I see in console the next text when task "images" starts:
"D:\home\projects\storyBook>gulp images
[15:05:23] Using gulpfile D:\home\projects\storyBook\gulpfile.js
[15:05:23] Starting 'images'..."
But when task is finished I do NOT see the next text:
"[12:13:56] Finished 'images' after 5.72 s"
Why do not I get this text? I do streams merge and then return merged stream to have synchronous task. Maybe I do something wrong?
2) If I add one code line to my privous code:
streams.allThemeImages = plugins.merge(streams.themesImages);
return streams.allThemeImages.pipe(gulp.dest('temp/')); // HERE IS NEW CODE LINE
I expect that in temp folder I'll have the next images:
temp/
1.png
2.png
3.png
4.png
Because I merged streams, first one contains 1.png and 2.png images and second one contains 3.png and 4.png. But in reality I get the next files:
temp/
1.png
2.png
What is wrong?