Change document strange

Hi!

We have recently updated SAP fomr version 4.7 to version 6.0

Now we have found strange Change Document in one PM WO. Rows do not show old / new value.

We can't simulate it. It is about COBRB table.

Question: is it version-related or usual? Do you have such case in earlier versions maybe? Any idea why is it so?

THX!