`inference_triggers` says root is child node

[luke-kiernan]

When I try to run inference_triggers, I get the following:

julia> itrigs = inference_triggers(tinf)
ERROR: ArgumentError: it seems you've supplied a child node, but backtraces are collected only at the entrance to inference.

You can even see it in the docs. Is it that the docs are out-of-date and there's some other method I should be using? Or is this a legitimate bug?