SOAP sometimes ignoring Overall Schedule Quantity

Good afternoon,

Our website uses SOAP to create Sales Orders. For some reason it will occasionally not adhere to the "quantity pricing schedule - by overall schedule quantity" intended to give discount on all group items when the total quantity reaches 5.

Example when using NetSuite UI:

Item 1 - Quantity 1 - 10% discount

Item 2 - Quantity 2- 10% discount

Item 3 - Quantity 2 - 10% discount

Item 4 - Quantity 3 - 10% discount

Occasionally from SOAP:

Item 1 - Quantity 1 - full price

item 2 - Quantity 2 - full price

Item 3 - Quantity 2 - 10% discount

Item 4 - Quantity 2 - 10% discount

In example 1, the rate for Item 1 and 2 will be full price until you input item 3 and the total quantity reaches 5, at that point all item rates will be discounted. When using SOAP for the same items it will sometimes, but not always, only apply the discounted rate to the line that makes quantity reach 5 onwards. The website/SOAP is currently handing the line amount to NetSuite so the customer gets billed correctly but it does cause some questions as to why rate * quantity /= amount. Is there some way we can fix this?