Oracle Change Data Capture: Unsubscribed column results in change set record
I imagine you've enabled suplemental logging for the table on all columns, instead of just the ones that you require to be tracked.

eg:

ALTER TABLE philtest ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;


vs:

ALTER TABLE philtest
ADD SUPPLEMENTAL LOG GROUP log_group_philtest
    (PHIL_COLA, PHIL_COLB) ALWAYS;