I've noticed that the mac app has the (old) directory icon used in previous versions.
On closer inspection I see that the icon has been correctly set, only the icon is overridden on the app itself (you can do this in the Finer > Get Info).
I've seen this before and I believe your DMG Packager automatically applied the icon on the directory on previous versions. Since the app replaces the directory, it seems that it puts the icon on the app instead.
Maarten @ Yesplan