Setting icons for Webapp

Using the appearance section of the IDE for my webapp. Created different versions of my app icon using Adobe Illustrator - exporting images for web as .png files. Drag and drop these .png files to the appropriate location in the appearance section icon boxes (for the various sizes/resolutions). When I drop the 32-bit, 32-pixel icon into its box, it automatically overwrites all the lower res icons. Similar behavior with the 48-pixel version, overwrites other entries. Is there some guidance on how to properly use this portion of the IDE?

Which version and platform of the IDE are you using?

Xojo 2013.4
Windows 8