The choir of which I am a member has learned, some time ago, O Salutaris Hostia, of Pierre de la Rue.
I've been helping a fellow choirmember re-learn the piece.
According to the edition I have, in the last bar of the piece, the syllable "li" of the word "auxilium" in the highest part falls on the semi-breve, instead of the crochet preceding this semi-breve. It seems plausible to me that, given the compositional techniques of the time, the syllable "li" should start on the crochet instead of the semi-breve.
I will try to find a copy I can load to this page to illustrate the point.
It would certainly be consistent with English syllabification habits. But then, la Rue wasn't..... But then, they all...... I think that your instincts are right.
We sing from the Castro edition on CPDL, and just do it as written, and I never found anything unseemly about it. (Note values halved, minim and quaver, so it is the same syllabification you mention in your post.)
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