Unexplained behavior on reimporting of MS Project

[shajhj8]

Hi, we have unexplained behavior on reimporting of MS Project with 2
different scenarios:

1. Reimport the same MS Project will overwrite project task that has been
updated.
2. Import to Siebel, Export back to MS project and reimport based on export
file will NOT overwrite project task that has been updated.

Below is the example:
Scenario 1:
1. Import ProjectTemplate_Baseline.mpp to Siebel using Task Only mapping.
2. Update Final Protocol - Actual Start and Actual End dates to 19 Oct 2006.
3. Update PostTrialtoClinicalTrials.gov - Planned Start and Planned End
dates to 20 Oct 2006.
4. Reimport the same ProjectTemplate_Baseline.mpp to SIebel using Task Only
Mapping.
5. Notice that All dates that were updated in # 2 and # 3 were replaced by
the reimport MS Project file.

Scenario 2:
1. Import ProjectTemplate_Baseline.mpp to Siebel using Task Only mapping.
2. Update Final Protocol - Actual Start and Actual End dates to 19 Oct 2006.
3. Update PostTrialtoClinicalTrials.gov - Planned Start and Planned End
dates to 20 Oct 2006.
4. Create a new Plan INtegration and Export to MS Project using the same
Project Mapping - Task Only mapping - see March14_SR2.mpp
5. Open Exported MS Project file and update PostTrialtoClinicalTrials.gov
start and end date to 10/23/07
6. Save March14_SR2.mpp
7. Import March14_SR2.mpp into Siebel using Task Only mapping using the same
Plan integration where this was exported.
8. Notice that Final Protocol actual dates were not changed

Question: What are these 2 scenarios produce different results?