Nunit integration

If you have a project referenced all three nunit assemblies and you put all dlls in the same folder.

like c:\unit_test
                       A.test.dll
                      nunit.core.dll
                      nunit.core.interfaces.dll
                      nunit.framework.dll

If I run the unit test with "Nunit2" task. everything seems fine. I can get the on-the-fly test result.
If I run it with Nunit addins ( nunit 2.4.8). everything seems fine except I can't get the on-the-fly test result. I use nant with ncover or partcover. If I delete the " nunit.core.dll" and "nunit.core.interfaces.dll" at that folder. I can get the  on-the-fly test result again.

it hanppend at all teamcity 4.1,4.5 and 5.01 too. any idea?