BUG: All upgrade prices are wrong if customer changes billing cycle

[stormy]

Please read carefully if you use monthly and yearly pricing for your products. Unless the price is the same no matter what the cycle (i.e. no discounts for yearly billing), most of your upgrade orders will have wrong pricing.

I've been trying unsuccessfully for WHMCS to recognize this as a bug. I thought I'd bring it up for discussion to see what everyone thinks. I encourage you to create a test user and try it on your install. It's a lot easier to see it with your own eyes than reading my explanation.

I just had to refund 20 bucks to a customer due to this.

Quick summary:

-Upgrading from Monthly to Yearly: the customer is charged LESS than he owes.
-Upgrading from Yearly to Monthly: the customer is charged MORE than he owes.

Any upgrade that changes the billing cycle will have a wrong amount, unless the "price per day" of the cycles is exactly the same.

How to test:

1. Create two products: one with monthly billing and another one with yearly billing. Put the due dates a month and a year in the future, minus a couple days. So this is equivalent to a customer placing an order a couple days ago.

2. Now let's see what happens when this customer wants to upgrade his plan. Login as the customer and go to the Yearly product. Go to the upgrades page.

3. In the upgrades page, choose an upgrade package. The Monthly billing cycle will already be preselected for you. Continue.

4. In the next page you will see a wrong price, which is higher than the customer should pay. Why? Because the amount is calculated using the monthly price! WHMCS will figure out the price per day of the monthly product and multiply it per 363. The due date never changes.

5. Go back, and choose the same product and Yearly billing instead: you will get the correct price, which is lower.

6. Now test the same with the Monthly product, and upgrade it to Yearly: the price is wrong again, but this time is lower than what they'd pay if they stay at Yearly.

Thoughts?