Would using 3D planes with Images on them not avoid this issue? [Although I have found transparency issues on objects with using Dark Clouds running]
Just a suggestion...
But have you resolved this yet?
I believe the creators of DC have moved onto a new product and as such DC may be discontinued, I could be wrong however, try contacting them about the sprite issue...
You can find them here
http://simul.co/ with a lovely landline number which if you have free Skype minutes you can use Skype to call them for free
Funny enough they are just down the road from me in Liverpool
Please do let us know if you do contact them!