Hi,
What is happening here is collisions of time constraint classes for the actual time types, not the infotypes. These are controlled via table V_554Y_B and the time constraint class entered in each time type in V_554S_O.
In V_554Y_B you determine the reaction when one absence type - say sick leave is entered on the same date as another type - say vacation. The reaction could be - A: Old record delimited and collision displayed, E: Error-new record not created, N: New Record Created but old record remains no collision displayed, W: New record created and old one remains but collision displayed.
You will have to examine the entries in both tables and determine what you want the reaction to be depending on the absence types in IT2001 vs. the entry in IT2011.
Paul