That's because only the operations that used a flag called that method. IOW, only those that needed forcing to return the previous value, e.g. put...etc. You could expand that to call this method for other operations and apply the flags if passed. There's two options you can take here then:

a) You could try to pass in the op code too and based on that decide if the flag makes sense for the operation or not, and create an advanced cache or not with it.
b) Based on the flag passed, get the cache with flags appropriate. If you pass a IGNORE_RETURN_VALUES to a get operation in cache, I'd imagine it would ignore it?

The first option might be better to avoid creating decorated caches unnecessarily.