IRC § 1361(b)(3)
No Termination of QSub Election on Stock Transfer Between QSub and Parent
Moving a lower-tier QSub’s stock from one QSub up to the common S corporation parent does not terminate the QSub election, because the parent is treated as owning the stock before and after.
Treas. Reg. § 1.1361-5(a)(4), Example 3 • Qualified Subchapter S Subsidiaries