System.Runtime.Caching.MemoryCache strange behavior?

Have this question up on the MSDN forums too (http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/0a666d5e-9bda-47bd-8dd3-98d32eb5fe60/?prof=required), thought I'd get an opini开发者_JAVA百科on of folks here :

Here's the output of my immediate window :

(EmployeeCache as MemoryCache).Add("test", new Object(),DateTimeOffset.Now.AddMinutes(10));
true
(EmployeeCache as  MemoryCache).GetCount()
0
(EmployeeCache as  MemoryCache)
{<namespace>.CustomCache}
[<namespace>.CustomCache]: {[<namespace>.CustomCache}
base {System.Runtime.Caching.ObjectCache}: {<namespace>.CustomCache}
CacheMemoryLimit: 1887436800
DefaultCacheCapabilities: InMemoryProvider | CacheEntryChangeMonitors | AbsoluteExpirations |   SlidingExpirations | CacheEntryUpdateCallback | CacheEntryRemovedCallback
Name: "keyname"
PhysicalMemoryLimit: 99
PollingInterval: {00:02:00}

Under what conditions will adding to a MemoryCache return true, but an object will not be cached? (The call to GetCount and the one following it are made immediatley after adding to the cache)

The easiest way to get into this situation is to Add on a MemoryCache object for which Dispose has been called. You can check this by using the Visual Studio debugger to see the private _disposed property of the MemoryCache object. Hover over a variable that references the cache, use a quick watch, or use the immediate window.