Ticket submitted before I could post the error message and reproduction steps.
When a method is defined as:
class Some::Class {
method foo (--> Int) {...}
}
...calls to the method will produce an error:
Unexpected extra argument (bless(do{\(my $o = 1)}, "Some::Class")) in call to method foo at ...
The same method, defined with an explicit invocant, will succeed:
class Some::Classs {
method foo ($self: --> Int) {...}
}