This is normal behaviour in CAEmitterLayer. It uses a different coordinate system than the rest of iOS. As it was a technology derived from MacOS its origin (0,0) is located at the bottom left, while in iOS the origin is located at the top left. When the picture gets drawn it causes the image to get flipped. CAEmitterLayer was not really designed to use images like that, mostly made for particle systems that do not require a specific orientation.
The simplest solution to this would be to flip the image yourself so when CAEmitterLayer flips it again it will appear like you want it. This might have gotten changes in iOS7 so you would have to do a version check and apply the correct image.
You could also flip it in code if you wanted. This is a short code that does it:
UIImage *flippedPicture = [UIImage imageWithCGImage:picture.CGImage scale:1.0 orientation:UIImageOrientationLeftMirrored];
Source: http://www.vigorouscoding.com/2013/02/particle-image-gets-mirrored-by-uikit-particle-system/