If you dig a bit into how to detect/measure a batteries fill state, you will realise that it is very difficult. One way is to measure the used charge, but this is very difficult and you will have to know exactly how much capacity the battery has.
The other, more common way, is to measure the voltage.
Its a simple fact that the voltage will raise again, after the load dropped.
So its not only BMEs fault, its simply a physical imitation.
How ever, as I said, it shouldn’t be more than some percents.