AddInStore.Rebuild blocks

I am using System.Addin and the method

   AddInStore.Rebuild(string)

That method ends up blocking - (not returning in multiple tests up to 12 hours.)

This happens on two completely different computers, with two different sets of hardware but the same OS - XP.
Removing components in the Addin tree eventually causes failures (exceptions) but nothing that I have been able to tie to the block.  The necessary host, etc addin dlls have been rebuilt multiple times with no problems.
Removing the .store files has no impact.
It blocks while running attached to the debugger in the IDE and when not attached.

The code is surrounded by a try/catch which logs every exception and nothing is reported. And running in the IDE indicates that there is no uncaught exception as well.

Via debugging the block is traced to the following (consistently)

[In a sleep, wait, or join]
mscorlib.dll!System.AppDomain.Unload(System.AppDomain domain) + 0x47 bytes
System.AddIn.dll!System.AddIn.Hosting.Utils.UnloadAppDomain(System.AppDomain domain) + 0x20 bytes
System.AddIn.dll!System.AddIn.Hosting.AddInStore.Discover(string assemblyFileName, System.AddIn.PipelineComponentType componentType = Contract, System.AddIn.Hosting.PipelineDeploymentState state = {System.AddIn.Hosting.PipelineDeploymentState}, string rootD...
System.AddIn.dll!System.AddIn.Hosting.AddInStore.BuildPipelineCache(string rootDir = "...\\AddinRoot", System.Collections.ObjectModel.Collection<string> warnings = Count = Cannot evalu...
System.AddIn.dll!System.AddIn.Hosting.AddInStore.RebuildImpl(string pipelineRootFolderPath = "...\\AddinRoot", bool demand) + 0x10a bytes
System.AddIn.dll!System.AddIn.Hosting.AddInStore.Rebuild(string pipelineRootFolderPath) + 0xa bytes

As noted in the above the block occurrs in AppDomain.Unload()

Versions for the dlls above

mscorlib.dll 2.0.50727.3603
System.AddIn.dll 3.5.30729.1

My main concern is that it blocks.  I wouldn't care if it threw an exception (of any sort.)


Actual code call is as follows.

String[] warnings;
try
{
  warnings = AddInStore.Rebuild(pipelineRoot);
}
catch(Exception e)
{
  _logger.Error("MS AddInStore.Rebuild() Error", e);
  throw;
}