As I've not heard about this issue before I suspect there is some issue with your settings. Please send me an email detailing your export settings and exactly what issue you are experiencing and I'll try and troubleshoot. Just keep in mind that HD is the default setting (what you see in the preview) and 16-bit is a lower, more pixelated resolution and toggling this 16-bit setting does not affect the preview, it's only visible in the exported Spritesheet.