Updating / deleting job types

I see in document 1296180.1  that deleting obsolete job types is a two-step process. At this time, we are wanting to change the description of a few job types, and I assume the same is true for changes. I don't understand why adding a job type will simultaneously update the F08001 and the UDC table 06/G, but subsequent changes or deletions do not have the same impact. Can you tell me the bug # referenced in this document? (1296180.1)