Normal. Cutoffs on Model 12s (also 42s and 97s) do not function like those on 870s or Mossbergs.
You are far from the first person to ask about this, so don't feel bad. The rearmost shell in the M-12 magazine is retained by the shellplate below and by a projection at bottom of the bolt above. It is not retained by the cutoff!
So when the bolt is closed the cutoff is "open" so not to restrict that next round.
The purpose of the M-12 cutoff is to prevent another shell from following the one next in line, as that would result in a jam. Thus, in normal operation the cutoff closes as the bolt moves rearward.
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