Ah, still more fuel for my wild speculation! You have indicated the deparse-ing of tied( sub {}->() ), which is just as I expected; but I went back and checked the deparse-ing of tied sub {}->(), and it looks the same to me:

$ perl -MO=Deparse,-p -e 'tied sub {}->()'
tied({sub {
    
}
}->());
-e syntax OK
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I had assumed from the (ahem) reference to reference constructors that tie was gobbling up the sub {} before ->() could get at it, but that's obviously not the case. So: Since they deparse identically, why do tied sub {}->() and tied( sub {}->() ) give different error messages?