It turns out your suggestion works, BUT I had to upgrade my wiki from version 5.1.21 to make it work. So apparently there was a bug in the macro that was fixed since that version.
Also, since 5.2.5. the text in the docs about <> has changed. I know that because I once put the home wiki version on disk, in order to avoid downloading the entire wiki each time I want to look something up online. The text about <> there says that the parameter to change the name of the field to transclude (default caption) is called ‘caption’. The current version (5.2.7.) says it is called ‘field’, which of course does make more sense.
Lesson learned: upgrade more often, especially when encountering strange behaviour!