On my x86_64 linux box running the latest version of Rust from git (as of this morning):

fn main() {
    let bar: fn() = {|| };
    bar();
}

Causes a leak:

Unreclaimed object found at 0x1b5a6a0: ((), ())
leaked memory in rust main loop (1 objects)
leak: ./src/rt/memory_region.cpp:172: memory_region::~memory_region(): Assertion `false' failed.
Aborted

Obviously this isn't very useful code, but I was just getting started and playing around with closures when I came across it. This might be a dupe of #2036 but I'm not smart enough to know :)