As far as I know, CBR with MPEG2 has never worked correctly. The results of PD15 720p set at CBR still produces a file with VBR.
Reproduced same file using CVBR and I get the exact same results. Same file size, etc. CBR just doesn't work at all.
Intel i7 4770k, 16GB, GTX1060 3GB, Two 240GB SSD, 4TB HD, Sony HDR-TD20V 3D camcorder, Sony SLT-A65VK for still images, Windows 10 Pro, 64bit
Gary Russell -- TN USA