usb bootable flag not cleared by gparted but cleared by Windows

Question

Model: Lexar USB Flash Drive (scsi)
Disk /dev/sdb: 64.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  64.0GB  64.0GB  primary  ext4

With this disk inserted the system cannot boot because it is not a system disk but is being picked up by the boot.

I tried to reset the boot flag clearing the flag column in gparted 0.32.0 but after applying the change, the system still picked it up as a bootable drive.

I deleted the partition and re-wrote it. No difference.

I eventually managed to clear the boot flag by formatting in Windows 10.

There must be a way of doing this in Ubuntu. Is there a menu item in gparted that forces this? Or is there another utility I could have used?