Unity after change scene twice then release the texture memory

Hi all

i did an test on Unity

i create three scene(SceneA,SceneB,SceneC)

SceneA contain one sprite with one texture(5.3MB),

SceneB,SceneC only contain one button for change scene

i use Android device for the test .

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Here is the steps:

1·Start game from sceneB, the memory use for texture is 2.8MB (as i use NGUI for the button)

2·Change scene to sceneA, the memory increase to 8.2MB (2.8MB+5.3MB)

3·Change scene to sceneB, the memory still 8.2MB

4·Change scene to sceneC, the memory drop down to 2.8MB

SceneB->SceneA->SceneB->SceneC

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also i did another test:

1·Start from sceneB (2.8MB)

2·Change to sceneA (8.2MB)

3·Change to sceneC (8.2MB)

4·Change to sceneC again (2.8)

SceneB->SceneA->SceneC->SceneC

any idea why?

thanks.