Bad optical kerning for superscript "4"
When a superscript "4" follows a closing smart quotation mark, optical kerning is set to -60 or -70 depending on font. This is too close (basically a crash).
This is annoying for books with lots of endnotes, where superscript numbers usually follow quotation marks.
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Thomas Ernst commented
Here's a good example. (and in this case "crash" does not refer to a software problem, but is the way typographers refer to two characters or glyphs that are too close together or even touch)
You can see the default kern between the endquote and the 4 is -86. I have seen many worse instances where the characters are actually touching.