Steps to regenerate the issue:
1. Create a price rule.
2. Add a condition, select input 'Quantity', operator 'Is' and add the value '2' or any quantity more than 1.
3. Add an action, select action type 'Flat Amount Override' and add it's value.
4. Create a sale order:
i. Add product with quantity one to the order.
ii. Update the quantity to 2 or to the value entered in condition for quantity in price rule.
iii. Recalculate the order.
Expected result: Unit price should override to the amount added in action.
Actual result: It's not getting overridden to the amount added in action.