From: Libertium/asmsx-license-gpl#3

What steps will reproduce the problem?

• Assemble the next source:
  .page 1
  .rom
  .size 48
  .start INIT
  .db "PAGE 1"
  INIT:
  ret

  .page 2
  .db "PAGE 2"

  .page 0
  .db "PAGE 0"
  ; EOF

What is the expected output?

• Page 0 has no cartridge header
• Page 1 has cartridge header ("AB" + INIT + padding up to 16 bytes)

What do you see instead?

• Page 0 has no cartridge header, but bytes 3 and 4 are overwritten by INIT
• Page 1 has cartridge header ("AB" + padding), but misses INIT

What version of the product are you using?

• asMSX v0.16 WIP / v0.17 WiP.
  On what operating system?
• Windows 7 Starter.

Please provide any additional information below.

• Possible solution: .start directive should write INIT value where the .rom
  wrote the header, instead of 3rd/4th bytes of output file
  Bonus points:
• As .rom directive is already locating the header at page 1, should it ensure
  there is no cartridge header at page 0? (is a ROM with cartridge header in page
  0 legal?)
• Allow .rom directive to be preceeded by code, so the code can be in natural
  order: .page 0 / .page 1 / .rom / .page 2

Workaround:

• (note that, as there is no .rom directive, output file extension is .z80
  instead of .rom):
  .size 48

  .page 0
  .db $00, $00 ; (ensure no ROM header in page 0)
  .db "PAGE 0"

  .page 1
  ROM_HEADER: ; (manual ROM header)
  .db "AB" ; ID ("AB")
  .dw INIT ; INIT
  .org ROM_HEADER +$10 ; STATEMENT, DEVICE, TEXT, Reserved
  .db "PAGE 1"
  INIT:
  ret

  .page 2
  .db "PAGE 2"
  ; EOF