hook_update_N is not called

Debugging is using 8.1.1 while the patch is for 8.2.x. It would be nice to show how to reproduce this bug in 8.2.x but since it does not always occur I want to get it documented first. The PHP version is 5.6.20.

Some hook_update_N functions are getting called and some are not. For the "my_master" module the update hooks are getting called while for the "my_newsletter" the update hooks are not found. I do not know why some are found and others are not but we have had this occur twice for different people implementing update hooks for different modules.

In schema.inc the PHP function get_defined_functions() is called to get all the functions:

$functions = get_defined_functions();

Sorting and dumping the result for the my_newsletter module shows:

    [571] => my_master_form_alter
    [1086] => my_master_update_8001
    [1087] => my_master_update_8105
    [1088] => my_master_update_8111
    [572] => my_newsletter_help
    [573] => my_newsletter_mail

The update hook my_newsletter_update_8001 does not show up but the hooks for the my_master module are there. It appears that the my_newsletter.install file is not getting included. If you want to find the update hooks you had better include the .install file for my_newsletter! So add the line

module_load_include('install', $module);

Now the functions found are

    [571] => my_master_form_alter
    [1086] => my_master_update_8001
    [1087] => my_master_update_8105
    [1088] => my_master_update_8111
    [572] => my_newsletter_help
    [573] => my_newsletter_mail
    [1142] => my_newsletter_schema
    [1143] => my_newsletter_update_8101

Now I am getting prompted for database updates. There is no harm (except performance) in including this line to make sure the .install file is included.