Known issue, as you already found out. Even if that gets fixed, won’t help your case so…
You’ll need to use /bin/dd to write back the data on that MBR backup file.
dd if=/boot/home/config/settings/bootman/MBR of=/dev/disk/[...]/raw
You’ll need to adjust both the if= parameter (to point th the MBR you got on the USB drive), and the of= one to point to your particular HDD/SSD drive (as an example… in my case, that would be: /dev/disk/scsi/0/0/0/raw.
Please double check the parameters to dd, specially the of= one before you hit enter.
If that fails, /bin/writembr should write boot code good enough to boot the active partition on the given device (you can call it without parameters, it will ask you to confirm installation on the HDD it finds).
If even that fails, you can re-install BootManager, only add your Windows install, and configure it to auto-select that option with minimal/no delay.
Note: the MBR backup file ended up in the USB media, because that was what you were using at the time of installing BootManager. One could argue that that file should be copied to the final install partition (with a distinctive name enough, as to not clash with further backup files BootManager (from the final install) might create.