That's really strange as a mysqldump command is mysql and has nothing really to do with php nor moodle code ... only what's in the DB for the moodle.
From mysql dient using your DB for Moodle, what does:
show tables like '%tag%';
should show:
| mdl_quiz_slot_tags |
| mdl_tag |
| mdl_tag_area |
| mdl_tag_coll |
| mdl_tag_correlation |
| mdl_tag_instance |
Using command line and in the location of a mysqldump'd sql file for moodle, issue:
fgrep 'mdl_tag' mdl35.sql
That will show all the references to mdl_tag_X in the mdl_tag table contained in the dump.
For tag areas
fgrep 'mdl_tag' mdl35.sql |grep mdl_tag_area
one of the areas ... book ...
fgrep 'mdl_tag' mdl35.sql |grep book
If sql dump has no tag data or missing tag tables then makes no diff as to how one imports an sql or upgrades a Moodle.
Again ... very strange.
'SoS', Ken