I'm running into an issue with Magento's Cart Price rules in 2.1.2 which appears to be a pretty major bug. I've configured a rule to apply free shipping to items within a specific category. After opening a clean browser, I can add items from the "free shipping" and "not free shipping" categories of my store and shipping is calculated properly.
However, if I remove the free shipping item from the cart, the cart reverts to free shipping for the entire cart regardless of what items are added to the cart until the browser is closed and the cache is cleared. In other words, it seems that free shipping for the entire order is toggled at some point in the process.
This is a new store setup. The "free shipping" items are basically items which have shipping costs built into the price.