Change to a field value during an operation called via handle not shown

When one non-modal form calls an operation for a second or subsequent time in
another modal form via a handle, any updates to fields made during the
operation call will not be shown on screen until either the field gets focus or
a 'show' statement is called.

The first time an operation is called via a handle, and when the same operation
is called via an 'activate' statement, field updates are shown on screen as
expected.