Nunit reload progresses longer times

Newer versions of Nunit take progressively longer time to reload a project after a rebuild.
Version 2.5.5 does not have this problem.

Note that one of the versions below is the newest development snapshot available.
I tried that because there is at least on similar report which suggested that this
might have been fixed in a newer version.

OS: Windows 7 64 bit
Running: nunit.exe
Visual Studio: 2008 with Resharper

How I tested - start with Nunit GUI Console up.
    - Use "Rebuild Solution" in Visual Studio
    - Wait for "Reloading..." to appear in Nunit.
    - Count seconds until "Reloading..." disappears.
    - Run test once
    - Repeat

-------------------------
Nunit: 2.5.8.10295

Test Loader Settings
   - Assembly Isolation:
            Run tests directly in the Nunit Process
            Use a single AppDomain for all tests
   - Assembly Reload:
            Reload when test assembly changes
   - Advanced:
            Enable Shadow Copy

Nunit: Start - 1 second (it loads test dll)
Nunit: After build - 1 second reload
Nunit: After build - 2 second reload
Nunit: After build - 4 second reload
Nunit: After build - 7 second reload
Nunit: After build - 11 second reload
Nunit: After build - 20 second reload

After last test I verified that there is only one "nunit.exe"
in the task manager listing.

-------------
I also tried this with 2.5.9.10320 (default install)
I explicitly linked in the framework dll to the project.

Nunit: Start - 1 second (it loads test dll)
Nunit: After build - 1 second reload
Nunit: After build - 2 second reload
Nunit: After build - 3 second reload
Nunit: After build - 5 second reload
Nunit: After build - 9 second reload
Nunit: After build - 17 second reload

--------------
I also tried this with 2.5.5.10112 (default install)
I explicitly linked in the framework dll to the project.

Nunit: Start - 1 second (it loads test dll)
Nunit: After build - 1 second reload
Nunit: After build - 1 second reload
Nunit: After build - 1 second reload
Nunit: After build - 1 second reload
Nunit: After build - 1 second reload
Nunit: After build - 1 second reload

===================================================
Code I used for testing.

using System;
using NUnit.Framework;

namespace ProgressSlow020508
{
public class Class1
{
    [Test]
    public void Test01_ValidateClass()
    {
        int i=47;
        Assert.AreEqual(47, i, "It worked");
    }
}
} // End of namespace