SAP Note 19251 - Old transport requests are imported again

Symptom:

When you start an import with command "tp import all U1" (many) old transport requests, which have already been imported successfully, are imported again.
The command "tp showbuffer " did not display the old transport requests.

Cause and prerequisites

Not an error. Unconditional mode 1 is intended for the specific purpose of repeating the import of successfully imported transport requests.
The only confusing thing is that "tp showbuffer " does not display these transport requests. The reason for this is that they have already been flagged as completely imported.

Solution
Do not use unconditional mode 1.
The unconditional modes disable the rules of the Correction of Transport System, and should therefore only be used under extenuating circumstances. From Release 2.2B onwards, you do not need to use the unconditional modes at all, not even for client transports.