According to Section 11.1.39 of JPA 2.0 spec:
OrderColumnAnnotation Element "updatable" means:
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider
Also in the same section:
The order column must be of integral type. The persistence provider must maintain a contiguous (non-sparse) ordering of the values of the order column when updating the association or element collection. The order column value for the first element of the list must be 0.
Two scenarios when an element collection is updated:
(1) a new element is added:
OpenJPA will execute an insert statement
(2) an old element is removed:
OpenJPA will perform delete/insert
For scenario (2), the operation is working as design in order to preserver the contiguous ordering of the values of the order column. In addition, no "UPDATE" statement is issued in this operation, which is consistent with what the spec says.