Joaquin M Lopez Munoz wrote:

You've got to implement semantics equivalent to that of the < relationship between numbers:

http://www.sgi.com/tech/stl/StrictWeakOrdering.html

Ah ha! After some serious unit testing, I uncovered a case in my sorting logic that does not comply with the strict weak ordering requirement. I have now fixed the logic, and I am no longer getting the invariant assert! Sorry to send you all on a "wild goose chase". I did consequently run into a SAFE_MODE related exception where an iterator to one of the indices was going invalid after an 'erase()' was called, and I'm still having problems with shared_ptrs, but I'll save the details for another discussion. Thanks for all of your help!