This behavior is specific to IBM JDK (I tried JDK6 and 7), it works fine with Java HotSpot.

Steps to reproduce the problem:

1) set maxEntries for eviction to 2 and algorithm e.g. to LRU
2) store 3 entries key1, key2, key3 to the cache (after that you can see that the cache contains only 2 entries - key2 and key3, the first one was evicted from memory)
3) call cache.get("key1")
4) PROBLEM - cache contains all key1, key2, key3 even though it should contain only 2 entries - only happens with IBM JDK (6 or 7 ..no matter)

I'll shortly issue a pull request with a test to ispn-core