With a user query similar to:

SELECT DB.Address, DB.City, count as Count FROM "Emp"."persons" as DB
GROUP BY DB.Address, DB.City
ORDER BY DB.City

If the grouping is pushed, but the order by is not an AssertionError will occur:

java.lang.AssertionError: Assertion failed.
at org.teiid.core.util.Assertion.failed(Assertion.java:73)
at org.teiid.core.util.Assertion.assertTrue(Assertion.java:68)
at org.teiid.core.util.Assertion.assertTrue(Assertion.java:60)
at org.teiid.query.processor.relational.SortUtility.<init>(SortUtility.java:145)

It does not occur if neither or both are pushed.