Comment 11 for bug 45292

This isn't debconf's responsibility; debconf is a generic framework for asking questions, and already provides maintainer scripts all the necessary knowledge to handle this kind of situation themselves. The maintainer script using debconf should catch non-zero return codes from db_input and print a better error message.

(Blaming debconf for this is a little like blaming the C compiler because somebody displayed an unclear error message with printf()!)