I've never seen this.
FAQ 4.15 describes using a serial console ... if you have access to the appropriate equipment you could obtain your dmesg via serial console.
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Since the keyboard works for the second stage bootloader, you could try disabling ACPI:
boot> disable acpi
boot> quit
Not-quite-standard ACPI implementations cause many sorts of problems; yours might be ACPI related. It's a hope, though, not a foregone conclusion.