Why is changed file not in output when using gulp.watch

[jensschneider]

My setup

index.html

@@include('./file1.html')
@@include('./file2.html')

file1.html

hello from file1

file2.html

hello from file2

Initial gulp process without .watch

result

hello from file1
hello from file2

Starting gulp.watch to index.html

Changing file1 to updating file1

result

hello from file2

Content of file1 is missing

Then changing file2 to updating file2

result

updating file1

Changings of file1 are included. Content of file2 is missing.

Stopping gulp.watch an run manually

result

updating file1
updating file2