Assertion monitoring in concurrent threads could be broken if
process-relative run-time variables are used to record current assertion
monitoring state instead of thread-relative ones. Assertion monitoring
state is changed either by entering an assertion clause (assertions are not
checked recursively) or by executing "magic" run-time code (like the code
for "clone" or "twin" defined in terms of "copy", when class invariants
should be temporary disabled).

Discovered in release 5.6.0503 for .NET code generation.