Odd unit test breaks using Test With...Coverage in TestDrive

I'm not sure if I should cross-post this to Jamie Cansdale or not, but thought I would start here.

I have been trying to integrate NCover into my MSBuild process. I started seeing unit test failures within the NCover process which I hadn't seen running the unit tests before.

Unit Tests Succeed With:

TestDriven.NET "Run Tests" option
TestDriven.NET "Test With...Debugger" option
TestDriven.NET "Test With...In Proc" option
MSBuildCommunityTasks NUnit MSBuild Task
nunit-console.exe from the command line

Unit Tests Fail With:

TestDriven.NET "Test With...Coverage" option
Grant's NCover Custom MSBuild Task
NCover.console.exe from the command line

The version of nunit-console is the same in all cases. 2.2.8, the .NET 2.0 version.

I'm running NCover 1.5.5 beta.

It almost appears like the exception handling is not working as expected. The specific tests that are failing are set up to trap a custom exception, yet the type of exception returned is a different type of custom exception from further up the chain. This includes both checking for [ExpectedException()] as well as trapping inline via try/catch blocks.

I've tried blowing away the /bin and /obj directories with no luck.

Any help is appreciated.