Can't use png-24 with `ionic resources`

I’ve got an icon which I export from Illustrator separately for Android & iOS. The iOS version keeps the background color (for the nice rounded corners effect), and for Android I disable the background & use alpha. Now, when exported as png-8 it works just fine with ionic resource. However, png-8 doesn’t seem to support the dropshadow, which png-24 does. But when I run ionic resources against the png-24 image, I get Invalid upload: unable to read uploaded image