I doesn't surprise me. I once typeset a book on the etymology of the word 'fiddle' which had footnotes that, in places, not only took up 80%+ of the page but some that contained diagrams. I had to draw a line at the footnotes that contained footnotes though.
As much as I'm usually opposed, that sounds like a time when you should switch to end notes. If your footnotes are extremely detailed and one can read your paper without them, put them at the end for those who care about all those details so that more casual readers can ignore them.
And if you have that high of a footnote:content ratio and don't believe that one can read the paper without the footnotes, then I think it is time to revisit what belongs in the footnotes vs. in the main content.
