Thumbnails of image files overwrite previously printed thumbnails

While using ember-collection I found one issue. Lets say I am showing contents (image files) of a folder using ember-collection. Folder has 1000 image files having thumbnails of each image file. Now when user scrolls down for the view to paint next page images then, the boxes created by ember-collection overwrites thumbnails of new image files over the previously painted (1st page) instead of writing on blank area.