For some reason I’ve ended up with a bunch of references that have the following: “R{ényi entropy”. This gets exported as is in the bibtex which is fine since the delimiters in the bibtex file are quotes. The resulting fields (title and abstract typically) will then play havoc with latex because of an unmatched bracket. Not sure why that particular metadata got imported but I guess the fields should not be trusted anyway.
Is it possible to sanity check the fields before export, and either escape the bracket (difficult to do consistently) or warn the user of problematic fields? Otherwise it’s a problem waiting to strike.
That’s a borderline case between bug and feature. Paperpile allows you to write LaTeX code in the title and book title field. That makes it easy for example to write the chemical structure of water as H$_2$O and it will be displayed correctly styled in Paperpile.
We also allow to use “{” and “}” to mark words where the capitalization should be preserved. If you really need a “{” or “}” character in your title you need to escape it with a backslash like “\{” or “\}”. On BibTeX export, Paperpile will do this escaping automatically for any field except the “title” or “book title” field. Any “{” or “}” in the abstract field will get escaped automatically, while for the title field we assume that the user has put them there on purpose.
In your case it seems that the number of curly brackets is unbalanced. In that case it is a good idea to show a warning.