There are no categories other than the two you mentioned in the source of the form:
pkCategoryID |
fkCostCentre_ID |
fkCostCategory |
destruction_due_date |
2 |
2 |
1 |
2012.06.01. |
2 |
2 |
1 |
2012.06.01. |
2 |
2 |
1 |
2012.06.01. |
2 |
2 |
1 |
2012.06.02. |
10 |
2 |
2 |
2012.06.03. |
2 |
2 |
1 |
2012.06.04. |
2 |
2 |
1 |
2012.06.05. |
2 |
2 |
1 |
|
2 |
2 |
1 |
|
After Update macro looks up the first record that match the categoryID, so it only finds those that are present in the source, in this case 2 and 10, both belonging to Business West. If there were other categories in the source, my guess is that the filter should work fine, returning the first record of the selected category.