PR kern/60140 assistance required, laptop boot issue (a weird one)

Could any of you who understand the very early stages of PC booting
(using efiboot - including efiboot itself), please take a look at
PR 60140 and see if there's anything you can suggest (even to just try
to get more data).

It involves a laptop which hangs hard at boot time, before starting
autoconfig (seemingly after loading the kernel) - but only when the
AC adaptor is plugged in (and not 100% of the time then).

To me that suggests either the final stages in efiboot, before handoff
to the kernel, or the very early stages of the kernel, probably before
it gets to the C environment.   All way outside my area (I have always
detested PC hardware, even though I use it, and so have never been even
slightly motivated to learn anything at all about it.)

I can't even begin to imagine what difference having the AC adaptor
connected can possibly make at that stage (if it were reversed, and not
having it connected was the problem, one could imagine battery problems
or similar, but not when the issue is when it is connected).  Connecting
it after NetBSD autconfig has started is harmless - only when connected
as efiboot transitions to the kernel is there a problem.

Thanks all,

kre