Maintain Baseline-Last Update Date field is empty (P6.7 SP4)

Hi,

I suspect that the Official Baseline of my project was changed.

When a baseline is created, the field called "Last Update Field" is updated and filled in.  Now that I started to look closer, there were several project baselines on the list that do not have any date under the "Last Update Field".

This is the first time I noticed it.

1) What can be the problem? In my opinion, this should always be updated even especially if one restored an existing baseline, update it and then bring it back.

2) Is there a way to trace who changed the baseline?