I've found the bug! (at least for me)
In the substance material parameters, you can't have any parameters with customised minimum values!
If a minimum value is anything else other than 0, every time you open it, it will reset that parameter to the minimum value you set it up.
So imagine you made a float1 scaling from Min5 to Max10 and you place it on the value 8. Every time you touch the material, it will automatically reset the value to 5!!!
quite stupid...