Cart line keeps base-currency price after switching currency add/remove sequence (variable product with Pre-Orders)

Plugin version: 2.4.2
WooCommerce version: 10.9.4

Also active: WooCommerce Pre-Orders (official, v2.3.4)
Cache plugin: Hummingbird Pro (WPMU DEV) is active on this site.

SUMMARY
A cart line item retains its base-currency price after the cart currency is switched to a secondary currency, causing the wrong-currency amount to carry through to checkout.

AFFECTED PRODUCT TYPE
Variable product (format/type variations via dropdown) that is also a WooCommerce Pre-Order product.

STEPS TO REPRODUCE
1. Set site currency to Currency A.
2. Add a variation of the product to cart.
3. Switch site currency to Currency B.
4. Add the same variation to cart again.
5. Remove one of the two resulting line item instances from the cart.

EXPECTED RESULT
Remaining cart line reflects the currently selected currency, with price correctly converted using the FX rate.

ACTUAL RESULT
Remaining cart line keeps the base-currency price under an order placed in the secondary currency — looks like the conversion step is being skipped for that line rather than a wrong fixed price being pulled.