windows qemu-img fails to convert vhdx, assertion failure

When attempting to convert Microsoft's 10X emulator image (19563) vhdx [1], qemu-img terminates abruptly with an assertion failure. (Newer versions of the vhdx exhibit the same issue.)

Tested with qemu-img.exe --version
qemu-img version 4.2.50 (v4.2.0-676-g3a63b24a1b-dirty)

Possibly related: 1719870

Partial Powershell cmdlet output:

PS> Get-Vhd flash.vhdx

VhdFormat               : VHDX
VhdType                 : Dynamic
FileSize                : 8365539328
Size                    : 137438953472
MinimumSize             : 137438953472
LogicalSectorSize       : 4096
PhysicalSectorSize      : 4096
BlockSize               : 1048576
ParentPath              :
DiskIdentifier          : 7BE7C459-AE5D-451A-9368-05875120F702
FragmentationPercentage : 11
Alignment               : 1
Attached                : False
DiskNumber              :
IsPMEMCompatible        : False
AddressAbstractionType  : None
Number                  :


[1] https://1drv.ms/u/s!AnjdAnZZcu-GpNFK_-tcNAq_4Aug8w?e=5JB6s0