`@source` annotation converted to a transclude sometimes

[ChrisPenner]

In #4610 @SystemFw noted that @source{foo} sometimes gets transformed into {{ docSource [docSourceElement (docEmbedTermLink 'foo) []] }}, e.g. here

I wasn't able to reproduce it, so just tracking the issue here. If anyone discovers a reproduction please add it here 👇🏼 !

[sellout]

This is similar to (but perhaps not a duplicate of) #2860 – Doc syntax getting pretty-printed as a Transclude. The docs linked in the description have a number of other examples, like

{{ docLink (docEmbedTermLink do day03.README) }}