Playing devil's advocate...
Such { curly brackets } are not illegal in Footnote or Short Footnote text so do not necessarily indicate a 'fault'.
A casual observer unfamiliar with Source Template Format { curly brackets } may think they are genuine.
e.g. \{ can be used in include an explicit { bracket.
If Citation-specific fields are used in constructs such as <{code1}|EMPTY!> or <{code1}|{code2}|{code3}> what gets returned bearing in mind each field code could be Citation or Source specific?
Note that those constructs return different text depending on whether fields are blank.
It looks quite tricky!