[perl #126426] Post-defined stubbed class not found if its name starts with an existing namespace

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# New Ticket Created by  Sam S. 
# Please include the string:  [perl #126426]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=126426 >


This compiles and runs fine:

    class A::B { ... };
    
    say A::B.new;
    
    class A::B {
        has $.a = 42
    };

But this fails to compile:

    class X::B { ... };
    
    say X::B.new;
    
    class X::B {
        has $.a = 42
    };

The error message is:

    The following packages were stubbed but not defined:
        X::B

Same issue when it's called Grammar::B, Int::B, etc. - apparently any
compound class name that starts with an existing namespace, runs into
this problem.


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(perl6 version 2015.09-433-g26617f9 built on MoarVM version 2015.09-79-gee9fc2b)