There was a similar bug in the Ubuntu lock screen a while algo: https://bugs.launchpad.net/ubuntu/+source/unity/+bug/1308572

  When the screen is locked with password, if I hold ENTER after some
  seconds the screen freezes and the lock screen crashes. After that I
  have the computer fully unlocked.

I don't think using a bootloader password is a very common way of (attempting to) secure a computer. At least I have never used it nor thought it could actually secure my computer (at least without locking out the bios/uefi to allow booting from other media and enabling secure boot).

So on any of my PCs, you could just press F10 to get access to the grub rescue shell.

I think that bios/uefi passwords and disk encryption are much more commonly used to prevent unauthorized access to an intruder with physical access to the computer when it boots.

More likely "Walk up to a Linux system and find this issue isn't even relevant as a bootloader password is not even configured in the first place"