In the program below, Child typechecks, but Child2 does not. The problem is that Bin2 is not being found when checking the constraint on Child2. Child typechecks because Bin is being explicitly qualified and this appears to avoid the bug. This is a somewhat common idiom when writing code that uses generic frameworks in X10, so it should be fixed. Only marking as major priority since there is an easy workaround.
The error messages are:
I think the key is the first messages. Compiler was unable to find the type Bin2.