Is the field an Auto Enter field or Lookup field? If so, if you update the key field in the table occurrence relationship, it will update the field. If the auto enter field is a calculation, you might want to check the box to keep it from overwriting data if there is something already in there. Other possibilities are if you have a script trigger or some script that is running updates on it. Things may seem random, but they never really are. It is just a matter of understanding the behavior.
Another possible cause is that you have one or more duplicate primary keys. I would advise checking for that before anything else and sorting it out if you find any.
It is definitely not a duplicate primary key. That is actually the first thing I looked at as well.
The field IS a Lookup field. I am going to thumb around in there and let you know what I find.
Thanks for getting me going.
Not sure why I had it as a Lookup field as it didnt really need to be. I removed the lookup and I am going to see if that is the issue. Usually does it a few times each day so I will post in here if that did not fix it.
Thanks for the help