Why do multiple Android SoundPool.unload calls return true / false depending on the order?

Question

According to Android documentation , SoundPool.unload returns

true if just unloaded, false if previously unloaded

I create SoundPool, load 5 sounds and save the corresponding 5 sound identifiers. Then, before leaving the Activity, I call unload for each of these identifiers and finally call release . I experience the following:

• if I call unloading for each identifier in some order (the one that is returned from the card), I systematically get false for identifiers 1..4 and true for ID 5;

• if I call the unload in the same order as the identifiers where it is loaded, from 1 to 5, I systematically get false for all identifiers;

• if I call the upload in the reverse order, as when loading, from 5 to 1, I systematically get true for identifiers 2-5 and false for ID 1

Does anyone know why this is happening, and how to make it come back? My task is not to properly clean resources and in some memory problems after repeated reloading / unloading.