Potting soil with premixed plant food

Everybody must have noticed those soil bags with beautiful pictures of healthy plants on them. There is a sign in the corner :"with plant food". If you look inside - you will see little green granules mixed into the soil. Use this soil carefully! I managed to damage two of my plants with it.
It is possible that the mix itself is OK, I am sure the manufacturers use complex calculations to verify the ratio of ingredients. But here is a pickle: When you buy a 10L bag, you are not likely to use it all in one pot. It seems that those plant food granules are a bit heavier then bits of soil, and somehow they tend to move to the bottom of the bag. So when you open the bag and take first handfull of mixture, it will have the minimal concentration of plant food, while the last one will have mostly the plant food granules and just little bit of soil.
Now, I didn't get to the bottom of my bag (otherwise I would realize all this issue), but my Zebra plant, that I re-potted fourth from the top, got burned very badly. I guess that part of soil already had an excessive concentration of plant food.
There is another problem that might arise, although I am not so sure about that, didn't experiment with it: if the roots of the plant will come to direct contact with some of the plant food granules - something tells me that it can damage some plants too.
Once again, I am not saying that potting soil with added plant food is bad, but if you use it, don't repeat my mistake. Mix the soil from bag well to make sure that food granules deposited evenly through the mixture. Or limit it's usage to just the top of your pot, making sure that root ball has regular soil without plant food.