A couple of places in the code we allocate with make() but then use
append(), instead of copy() or direct assignment. This results in a
slice with len() zero elements at the front followed by the expected
data. The correct form for such usage is `make(struct, 0, len())`.

I found these by running:
```
$ git grep -EI -A7 'make\([^,]*, len\(' | grep 'append(' -B7 | grep -v vendor
```
And then manually looking through the results. I'm sure something better
could exist.