• Using VisualEditor, add a citation
• Select Manual
• Select Basic
• Insert "Harvnb" template
• Fill out parameters
• Save and add citation

What happens?:
This produces the following error:

[[#CITEREF|]], p. ''X''

What should have happened instead?:
Should produce:
^ Author last name, year, p. ''X''

Comment
I believe the issue is that the Harvnb template is filled out like so: {{Harvnb|author|year|p=X}}; but VisualEditor fills it out like {{Harvnb|last1=author|year=author|p=X}}. When a citation filled out like the former is copy-pasted in Visual Editor, the first two parameters are listed as "1" and "2" rather than "last name" and "year". When done that way, the issue doesn't seem to appear.