Adding a key to a group creates a new MemoryGroup containing only the new key. This is a wrong behavior in situaltions where a persistentGroup group exists (with potentially further keys). The key should only added to existing MemoryGroup.

Line 1482 in AbstractConcurrentReadCache:

Set memoryGroup = (Set) groups.get(groupName);

if (memoryGroup != null) {
                    memoryGroup.add(key);
                }