Hi,
This is something that today stack traced in our DEV environment (CS10.0 U2016-06) but I found the bug in CS 16.0 so I thought I'd raise it here. It has to do with the correct way to check a Record (not an Assoc) for a feature. See attached:

See the hilighted bit above. If a feature does not exist in a record trying to reference the feature results in an Error, not Undefined (which is the behaviour of Assoc).
Cheers
-Hugh Ferguson