Using New-VHD to create differencing disk based on AVHDX parent disk

Hi, I am trying to create a differencing VHDX disk based on a snapshot AVHDX disk.

The PowerShell command I am using is as follows:

New-VHD -Path abc.vhdx -ParentPath d:\vm\fs00\fs00_6ccd6d16-98d2-498f-94eb-1335ab0b1558.avhdx -Differencing

which unfortunately fails saying the AVHDX extension on the parent disk is not allowed:

The file extension for 'd:\vm\fs00\fs00_6ccd6d16-98d2-498f-94eb-1335ab0b1558.avhdx' is invalid.
Virtual hard disk for this operation must have a .vhd or .vhdx 
extension.+ CategoryInfo          : InvalidArgument: (:) [New-VHD], VirtualizationException+ FullyQualifiedErrorId : InvalidParameter,Microsoft.Vhd.PowerShell.Cmdlets.NewVhd

Preliminary research indicates that differencing disk can be based on other differencing disk, and also that AVHDX files are indeed differencing disks. Indeed, repeating the command after renaming the extension of the parent disk file from .AVHDX to .VHDX works!

Is this a bug in the New-VHD cmdlet? Or is using an AVHDX file as the parent of a differencing disk not supported for some reason?

Also would you have any suggestion for how I can workaround the bug? Renaming the AVHDX would be problematic.

Thanks for any help.