Ensemble3 specifies an image for its preview element's border:

.sample-medium-preview {
    -fx-border-image-source: url("images/tile-border.png");
    ...
}

When the main page is scrolled, corresponding Image objects are instantiated hundreds of times, which impacts scrolling performance as well as texture memory on GPU (especially important on embedded).
Relevant code is in javafx.scene.layout.BorderConverter.convert(java.util.Map), in "BorderConverter.java"