as @armadillu points out, this is already fixed in the nightly builds.
the copy of the functions is so ofEvent is thread safe. there's a new class ofFastEvent that doesn't do that copy or use any lock, which is significantly faster, but for normal use (ie: user interaction events like mouse, keys...) ofEvent is fast enough.
Usually an event won't have much more than a couple of listeners so that copy won't be that problematic but for cases where you need lots of performance, like audio... you can use ofFastEvent but then you have to synchronize if you work from different threads