[Not a bug] Have I just found a defect with Gift Certificates?

I had a small balance in my Gift Cert "account" - because sometimes when I take a phone/special order, I need to give the customer some sort of discount.
I had an order entered into the cart.
I emailed myself a gift cert. for a large balance, and redeemed the number while inputting this order.
I applied the amount I needed to the order, which was larger than the original balance, but smaller than the new gift cert.
The discount applied correctly to the order I was entering, but now my gift cert balance is the total of the two amounts BEFORE the cert was applied to my order.

Here's the math details.

I had a balance of $23.92 in my gift cert account.
I redeemed a $300 gift cert by entering the code on the order page.
When the cart went to the next page, it said I'd redeemed $300.00.
I then hit the back button so I could apply part of this balance.
The balance showed as $323.92.
I applied $38.88 to the order I was entering. It was applied correctly to the order.

Now my gift cert balance is showing up as $323.92,
NOT $285.04.
Looks like a bug to me.

1.3.9a.

I had a small balance in my Gift Cert "account" - because sometimes when I take a phone/special order, I need to give the customer some sort of discount.
I had an order entered into the cart.
I emailed myself a gift cert. for a large balance, and redeemed the number while inputting this order.
I applied the amount I needed to the order, which was larger than the original balance, but smaller than the new gift cert.
The discount applied correctly to the order I was entering, but now my gift cert balance is the total of the two amounts BEFORE the cert was applied to my order.

Here's the math details.

I had a balance of $23.92 in my gift cert account.
I redeemed a $300 gift cert by entering the code on the order page.
When the cart went to the next page, it said I'd redeemed $300.00.
I then hit the back button so I could apply part of this balance.
The balance showed as $323.92.
I applied $38.88 to the order I was entering. It was applied correctly to the order.

Now my gift cert balance is showing up as $323.92,
NOT $285.04.
Looks like a bug to me.

1.3.9a.

Moved to "bug report" forum.

That's not normal behaviour.

I've redeemed lots of Gift Certificates with varying balances already in the account, and the system normally does properly deduct the amount applied to a given purchase, so I'm puzzled about why it's doing something different for you.

What addons have you installed?
Is this an upgrade from a prior version? which version(s)? Or is it a fresh new install?
What payment modules are enabled? What order-total modules are enabled?
What are all the settings in your ot_gv order-total module?
Was this transaction paid-for in-full by the gift certificate? or was there a balance that was paid via some other module? which one?
If I am to attempt to recreate your environment and recreate the exact same conditions as yours, what do I need to do to my fresh clean install to make it function just like what you've described?

What addons have you installed?
Is this an upgrade from a prior version? which version(s)? Or is it a fresh new install?
What payment modules are enabled? What order-total modules are enabled?
What are all the settings in your ot_gv order-total module?
Was this transaction paid-for in-full by the gift certificate? or was there a balance that was paid via some other module? which one?
If I am to attempt to recreate your environment and recreate the exact same conditions as yours, what do I need to do to my fresh clean install to make it function just like what you've described?

Installed Add ons
Sales Report
Recover Cart Sales
Easy Populate
Lightbox
Ultimate SEOs
Blank Sidebox

Payment Modules:
Net1 payment module for Sage Payments

Looks like
Discount Coupon
Group Discount
Gift Certificates
Low Order Fee
quantity Discount
Shipping
Subtotal
Tax
Total
modules are turned on.

A well known Zen cart master did the upgrade - pm me for details -upgrade was from 1.3.8a to 1.3.9a. I'm not sure the method that was used. I believe it was new.

Transaction was not paid in full. I had a transaction of $300+ entered, had a beginning gift cert balance of $23 or so. I then (from another window) emailed myself the new $300 gift cert. I redeemed it through the order screen. I then hit the BACK button to apply around $38 gift cert. When I finished checkout, the "successful status" box in the upper right hand of the shop said my balance was $300 PLUS my original balance, not the correct balance.

please PM for info (url, person doing my upgrade).

Thanks!!!

So, you applied $38 gift certificate against the order purchase price. How was the rest of the order paid for?

Additionally, you just mentioned something about a "successful status box" on the end of checkout. I'm not sure I recognize that box.
If you go to your My Account section, what does it say about your gift certificate balance there? Is that the same as what you saw on the end of checkout?

Also, when you look at that order in your admin section, what are the order-total details showing? ie: subtotal, tax, shipping, gift cert, total. What are they, and what values/amounts do they show?