A couple of things were going wrong:
* they're creating CloneNodes (but not requiring the contents of the clone of the clone node to be temp)
* assignment from a clone node generates cleanup code (which is against the general rules of a clone node), and also loses a reference via giveref
* cpdef functions cause a small memory leak (#4412) by assigning to their constants twice. This is unfortunately difficult to test for. With this patch we no longer leak, but still duplicate a little bit of work.