The issue was caused by the image save operator ignoring Z-Buf if the input buffer due to the way how IMB_dupImBuf() worked. There's no reason to to ignore z-buf on imbuf duplication, it only asks for issues in the future.
The issue was caused by the image save operator ignoring Z-Buf if the input buffer due to the way how IMB_dupImBuf() worked. There's no reason to to ignore z-buf on imbuf duplication, it only asks for issues in the future.