Able to add same attribute combination multiple times in Product attribute combination. Also "Please select color" error

We found couple of bugs in the newly released nop Commerce version 3.9. Which is regarding attribute combination with quantities. Kindly find below my system environment.
1) Nop Commerce 3.9
2) Windows 10
3) Sql Server 2012
4) I didn't make any customization. I have just downloaded new source code and install it.

Now coming to bug.

1) We are able to add same attribute combination multiple times with different quantities.

1.1) Also once we have two same attribute combination and we purchase the product with that attribute combination it takes first attribute combination quantities and deduct it. But if we have zero quantities in that same attribute combination it shows out of stock even though we have same attribute combination with more than 0 quantities.

2) Suppose we have created 4 attribute combination with two attributes. Now, we are creating one more attribute but we can't add newly created attribute to the existing attribute combination and getting error message like "Please select [Newly created attribute name]". And if i want to add newly created attribute into the existing combination i can't do that.

I must have to cretae new attribute combination if we want newly created attribute in inventory.

I have attached couple of images here kindly find link below.
https://www.dropbox.com/sh/zho3wuow2uzlcwm/AAA4BYOpsUjcFIiWXf5ky_uVa?dl=0

Thanks a lot!

1. I've just created a work item
2. Not sure that it's possible to fix. In such cases combinations should be re-created (re-generated)

1. Done. You can see the changes in this commit.
Thanks for the suggestion.