When placing down Loamy Dirt or harvesting a tree, in this case an Oak tree, when the dirt becomes grass, it turns into default MC Grass rather than Loamy Grass ... im not sure if this is due to other mods i may have installed or its a BOP bug though

Vanilla trees place a vanilla dirt block below them when grown. There's nothing we can do about this sadly.

Ahh ok, so call it more of a Out of your control feature lol