Who can explain the strange behavior of gulp?

Question

gulp.js

There are 2 tasks (besides task-watcher):

var gulp = require('gulp');

gulp.task('watch', function () {
    gulp.watch('src/*.html', ['html']);
    gulp.watch('src/*.php', ['php']);
});

gulp.task('html', function () {
    gulp.src('src/*.html')
        .pipe(gulp.dest('app'))
});

gulp.task('php', function () {
    gulp.src('src/*.php')
        .pipe(gulp.dest('app'));
});

The first (html) responds well to adding new files , the second (php) does not, it only processes the existing ones before launch.
1) What could be the matter, why does it not work in the second case?
2) Why does it work in the first case? Is the standard gulp watcher finally able to react to adding files?
gulp v3.9.1
node v6.9.4