org.openide.util.ImageUtilities has many methods that create/convert images/icons. Many images/icons are cached for re-use when created, but when images are converted to icons or icons converted to images, new instances are created without caching. It seem fitting that the icon2Image and image2Icon would also use cached images/icons.
An example use would be to use mergeImage and then wrap the Image in ImageIcon. If image2Icon cached the resulting icon, multiple calls would not create multiple ImageIcons.
Seems org.openide.util.ImageUtilities is a part of the platform, so I'll re-assign this issue. Please, evaluate this bug.