poweroff command not working after memtest

[johnpaul]

I am using undionly.kpxe compiled with the POWEROFF_CMD line in config/general.h.

If I go to an interactive iPXE shell and type 'poweroff' it works fine.
If I then chain memtest with the following:

chain memtest.0 onepass onefail && set memtest GOOD || set memtest BAD

(downloaded from here: http://boot.ipxe.org/memtest.0) and then go back to the interactive shell and type 'poweroff' I get the following error:

Could not poweroff: No such file or directory (http://ipxe.org/2d90203b)

I get the same behaviour from within a script. Every now and then it does still work, but the majority of the time it gives the error above.
I can't determine if it's memtest that is breaking it or whether it's something else.
Anyone any ideas?