Grub 2.12 problem with vmnext3 network card and PXE

[Mathias Radtke]

Some of our vSphere VMs are using vmnext3 networc cards.
Grub2.12 is downloaded via TFTP onto the VMs. An embedded grub.cfg downloads a grub.cfg placed on a TFTP server.
However since Grub 2.12 this doesn't work anymore.

When executing the embeeded cfg the cursor stalls for a couple of seconds and returns to a grub shell.
Using debug=all I see a lot of malloc calls and:
kern/verifiers.c:212:verify:string configfile (tftp,192.168.1.1)/path/grub.cfg, type: 2
On the server side we do not see any TFTP requests.

Switching to an E1000e or UEFI Mode fixes the issue and the embedded cfg succeeds in getting the requested file.

Grub 2.06 works fine with vmnext3 in the same VM configuration.

Any suggestion/idea where this might come from?