Part-year members of a combined group.

If a corporation becomes a member of a combined group or ceases to be a member of a combined group after the beginning of the taxable year of the combined group, the corporation’s income shall be determined as provided under subs. (3), (4), and (5) for the portion of the year in which the corporation was a member of the combined group and that income shall be included in the combined report. The income for the remaining short period shall be reported on a separate return or separate combined report.