When running /install/upgrade_400a1.php?step=6, I see the following status messages. Note the repeat of "(13 of 14)" and missing "(14 of 14)".
Step 6) Attachment System Alterations (3/4)
* Altering filedata Table (1 of 13)
* Altering filedata Table (2 of 13)
* Altering filedata Table (3 of 13)
* Altering filedata Table (4 of 13)
* Altering filedata Table (5 of 13)
* Altering filedata Table (6 of 13)
* Altering filedata Table (7 of 14)
* Altering filedata Table (8 of 14)
* Altering filedata Table (9 of 14)
* Altering filedata Table (10 of 14)
* Altering filedata Table (11 of 14)
* Altering filedata Table (12 of 14)
* Altering filedata Table (13 of 14)
* Altering filedata Table (13 of 14)
* Altering attachmenttype Table (1 of 1)
* Altering filedata Table (1 of 13)
* Altering filedata Table (2 of 13)
* Altering filedata Table (3 of 13)
* Altering filedata Table (4 of 13)
* Altering filedata Table (5 of 13)
* Altering filedata Table (6 of 13)
* Altering filedata Table (7 of 14)
* Altering filedata Table (8 of 14)
* Altering filedata Table (9 of 14)
* Altering filedata Table (10 of 14)
* Altering filedata Table (11 of 14)
* Altering filedata Table (12 of 14)
* Altering filedata Table (13 of 14)
* Altering filedata Table (13 of 14)
* Altering attachmenttype Table (1 of 1)