Currently in Actions.java in the method getActionImage, the image is loaded from the org.adempiere.base bundles class loader by calling:
InputStream inputStream = Actions.class.getClassLoader().getResourceAsStream(path);
This has a disadvantage since you would either have to export action.images in your bundles manifest - which can cause split package problem when having 2 or more bundles for toolbarbuttons - or you have to create a fragment holding your images.
This could be solved by loading the image directly from the osgi bundle via the actions class loader (see patch)
With the patch you don't need to export your action.images package anymore