https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-core/src/main/java/com/jme3/renderer/RenderContext.java#L222

public final Image[] boundTextures = new Image[16];

Let's say for example an application uses maximum 14 textures in every material.
If during runtime the application changes to use max 13 textures, the 14 unit will never be touched again and the reference held by RenderContext will prevent the image object from beeing gced.

Possible fix: Use WeakReferences