From @TimToady

18​:17 <TimToady> m​: say [[2, [3,4]], [4, [5, 6]]]».[1]».[1]
18​:17 <camelia> rakudo-moar 271e84​: OUTPUT«(4 6)␤»
18​:18 <TimToady> m​: say [[2, [3,4]], [4, [5, 6]]]».[1;1]
18​:18 <camelia> rakudo-moar 271e84​: OUTPUT«Cannot call postcircumfix​:<[;
]>(Array, Int, Int); none of these signatures match​:␤ (\SELF,
  @​indices)␤ (\SELF, @​indices, :$exists!)␤ (\SELF,
@​indices, :$delete!)␤ (\SELF, @​indices, :$BIND! is rw)␤ in block
  <unit> at /tmp/09M2eEBp8Z​:1…»

This might be related​:

18​:22 <TimToady> m​: say [[2, [3,4]], [4, [5, 6]]].map​: *.[1;1]
18​:22 <camelia> rakudo-moar 271e84​: OUTPUT«Earlier failures​:␤ Index out of
range. Is​: 1, should be in 0..0␤ in block <unit> at
  /tmp/s1pOCoXHdJ​:1␤␤Final error​:␤ Cannot call map(Array​:
Failure); none of these signatures match​:␤ (\SELF​: █;
  :$label, :$item, *%_)␤ (HyperIterab…»

From @TimToady

Fixed with 23248109c9c93db2774fcc9ce0c849a73a01fdad
Tested with f8c0844fbffeac6022603cda8bfbc4f1f35e9a57

@TimToady - Status changed from 'new' to 'resolved'