Installing ReactOS to a previously bootcd/livecd flashed USB drive messes up its MBR

I first flash a recent bootcd/livecd to a USB drive. This USB drive is then bootable as the ISO gets a proper MBR through the isohybrid tool.

I then boot into ReactOS usetup from another drive and try to install ReactOS onto the previously flashed USB drive. Usetup allows me to delete the existing CDFS/ISO-9660 partition on that drive and install as usual into the now unpartitioned space. I let it install FreeLdr in the MBR and VBR.
The USB drive is not bootable afterwards though. It errors out with "No active partition found".

Even worse, popular partitioning tools freak out at this MBR too:

• DiskPart shows the partition but a "select partition 1" results in "No partition selected" on Windows 10. Therefore, you cannot delete it.
• Linux cfdisk (Ubuntu 16.04) fails to open the drive with "cfdisk: libfdisk/src/table.c:408: new_freespace: Assertion `start' failed."
• Linux fdisk (Ubuntu 16.04) shows a partition table as attached in fdisk-after-installation-to-fakembr-usb-drive.txt.

See the messy MBR attached: messed_up_mbr

I could only zero out the MBR of the USB drive and let ReactOS recreate a new one during installation. Installation to the USB drive then worked and ReactOS was able to boot from it afterwards