Minor issue while using sync cache

Thank you for writing an awesome caching framework. I was playing with it and noticed that the adding to the LRU cache after the items have expired results in an error. I have added a test to reproduce this issue. 

I wrote a temporary fix ( to work around this issue). Please feel free to reject this patch and fix it correctly, as I have not had time to look at the full root cause of this bug.

Thanks.