From @zoffixznet

The first one says it expected Int but got Str, when in reality the type constraint is Any-to-Int​:D coercer.

The second one talks about Int methods, but I ain't calling any. IMO the coercer should catch such errors when calling the method and report them as type check failure instead.

18​:34 Zoffix m​: sub (Int​:D()) {}( Str )
18​:34 camelia rakudo-moar fb7dd8​: OUTPUT​: «Type check failed in binding to parameter '<anon>'; expected Int but got Str (Str)␤ in sub at <tmp> line 1␤ in block <unit> at <tmp> line 1␤␤»

18​:34 Zoffix m​: sub (Int()) {}( Str )
18​:34 camelia rakudo-moar fb7dd8​: OUTPUT​: «Invocant of method 'Int' must be an object instance of type 'Str', not a type object of type 'Str'. Did you forget a '.new'?␤ in sub at <tmp> line 1␤ in block <unit> at <tmp> line 1␤␤»

Nowadays the output looks like this:

$ ./rakudo-m -e 'sub (Int:D()) {}( Str )'
Parameter '<anon>' of routine '<anon>' must be an object instance of
type 'Int:D(Any)', not a type object of type 'Str'.  Did you forget a
'.new'?
  in sub  at -e line 1
  in block <unit> at -e line 1

$ ./rakudo-m -e 'sub (Int()) {}( Str )'
Cannot create an Int from a 'Str' type object
  in sub  at -e line 1
  in block <unit> at -e line 1

The second evaluation fails with X::AdHoc. But in general the new behavior looks sensible to me.