f74973 introduced a regression where a node which has had an input
added, will clobber a converted input of in a workflow created before
the input was added.
The prior behaviour was also incorrect (the new input would not exist on
the node), but would often be runnable.
Keeping the position of the converted widget and adding the new input to
the end is an unfortunate compromise. Doing it the other way around
breaks primitive nodes
