Hello @wclansar and @ansarhusain, we tried to reproduce this issue by next case:

Clone magento from GitHub: git clone https://github.com/magento/magento2.git (this is "develop" branch)
Then switch branch to 2.0: git checkout -f 2.0
Install Magento 2 (with default values during web installation, sample data is not used)
After installation, login to admin
Go to Products > Catalog and click "Add Product"
Then fill all required fields for creating simple product:
Name = simple product
SKU = simple product
Price = 10
Tax Class = Taxable Goods
Quantity = 1
Categories = test (click "New Category" and create category "test" as child for "Default Category")
Save the product(all other settings in default state)
Go to Storefront as Guest (the same result if we use registered customer)
Click for open "test" category
Click "Add to Cart" button

Result:

Could you pls provide more information about Your Magento 2 and server settings, like

Which version of PHP do you use, php 7.0.4?
Do You use Varnish or not?
Do You use Redis or not?
Do You use HTTPS or HTTP for Storefront and admin?
Do You use Sample Data?
Which Magento 2 mode do You use? (default/develop/production)
Do You use Definition compilation Tool after installation?
Do You use Static Content Deploy after installation?
Do You use JS minification ?
Do You use JS Bundling?
Do You use JS merge?
Do You use HTML minification?
Do You use Flat Catalog Product?
Do You use CDN as Static Content?
Wich browser do You use? (Firefox/Chrome/IE)
Probably there is other specific configuration that we miss.

Magento2 Mini Cart Items Issue #4170

Description