Improvingworks Infinitest

I have many unit tests that use the simple Java 'assert' syntax. For example:

assert myVar!=null : "You var actually IS null!";

When using TestNG or JUnit normally, these asserts correctly fail tests. However, when run by Infinitest, these assertions don't seem to actually fail the tests when they should. I get all successes all the time. However, when I use the TestNG or JUnit 'Assert' classes, the same test correctly fail both normally, and when run by Infinitest. For example:

Assert.assertNotNull(myVar,"Your var actually IS null!");

Not sure if this is user error, but I'm not seeing anything in the User Guides or published documentation about it, and it's proving to be a pretty big problem for me at the moment.