MemoryCache item does not get added at all
===

I'm experiencing some difficulties while trying to use the .NET MemoryCache.

When I try to add an item:

    var cacheItemPolicy = new CacheItemPolicy();
    cacheItemPolicy.RemovedCallback = ItemRemovedCallback;                
    cacheItemPolicy.Priority = CacheItemPriority.NotRemovable;
    cacheItemPolicy.SlidingExpiration = TimeSpan.Zero;
    cacheItemPolicy.AbsoluteExpiration = DateTimeOffset.MaxValue;
    umoXUserCacheStore.Add(key, value, cacheItemPolicy);   

or
    var cacheItemPolicy = new CacheItemPolicy();
    umoXUserCacheStore.Add(key, value, cacheItemPolicy);   

No exceptions get thrown and Add returns true, but no item has been added. 
I find this very strange, and have absolutely no idea where to start looking for an answer. Especially since true gets returned and no exceptions get thrown...

Any ideas?

 