This is from page 248 in the 4.2.1 AIX Administrator's Guide.

Partial Incremental Backup
When a user requests a partial incremental backup, TSM performs the
following steps to
determine eligibility:
1. Checks each file against the user's include-exclude list:
? Files that are excluded are not eligible for backup.
? If files are not excluded and a management class is specified with the
INCLUDE
option, TSM uses that management class.
? If files are not excluded but a management class is not specified with the
INCLUDE
option, TSM uses the default management class.
? If no include-exclude list exists, all files in the client domain are
eligible for backup,
and TSM uses the default management class.
2. Checks the management class of each included file:
? If there is a backup copy group, the process continues with step 3.
? If there is no backup copy group, the file is not eligible for backup.
3. Checks the date and time of the last incremental backup by the client,
and the
serialization requirement defined in the backup copy group. (Serialization
specifies how
files are handled if they are modified while being backed up and what
happens if
modification occurs.)
? If the file has not changed since the last incremental backup, the file is
not backed
up.
? If the file has changed since the last incremental backup and the
serialization
requirement is met, the file is backed up.

This is from page 105 of the AIX Administrator's Reference

MODE
Specifies whether TSM backs up a file only if the file has changed since the
last backup,
or whenever a client requests a backup. This parameter is optional. The
default value is
MODIFIED. Possible values are:
MODified
Specifies that TSM backs up the file only if it has changed since the last
backup.
TSM considers a file changed if any of the following is true:
? The date last modified is different
? The file size is different
? The file owner is different
? The file permissions are different
ABSolute
Specifies that TSM backs up the file regardless of whether it has been
modified.
The MODE value is used only for full incremental backup. This value is
ignored during
partial incremental backup or selective backup.

The last sentence here and what the Administrator's guide lead you to
believe that mode has no play on a partial incremental.

I can see where this is going.  Tivoli will correct the documentation.
Actually this would be a nice feature.  The reason is that it makes the
product work like competitive products if the customer wants to operate that
way.  Fulls + incrementals.  From a marketing perspective it would give
customers a way to transition to TSM using their old philosophy and migrate
slowly into the TSM model.  There are clients that really need this type of
backup philosophy to make the users comfortable.