Bug in ObjectDiff isNoop? (4.2.M1-SNAPSHOT from today)

I was thrown today when a "header" object didn't run through its
validateForSave() method when adding or deleting objects from a "detail".
It appears that isNoop is true for the header object because no base
attributes get modified.  When one is modified it alters the modFound
variable which ultimately gets returned from that method.  In the case of
To-many relationships, this variable is never modified (nor is the
relationship checked).  In the case of To-one relationships, it does appear
to do the right thing (just reading the code).

Am I missing something?

Thanks!

-Lon