This morning I have a long list of items without preferred vendors. We require that all items have one, so I went looking for the reason and found that there had been duplicate vendors in our system and they were merged. I can see in the system notes that the preferred vendor was changed:

But a saved search on this record returns null for Preferred Vendor, despite the Preferred box being checked:

I also have a custom field that displays the preferred vendor value in the main area of the item record, and it is now blank.

Is this a known issue when merging vendors? Is there a simple way to resolve it? If I edit and re-save one of these items the problem is fixed, but doing that for each item would take a long time.