For weeks I have had problems with a debian/postinst that did not to finish. This made debconf’s frondend hang around waiting, and the ‘aptitude upgrade’ process never finished. The workaround was to restart the program (NAV), which in a wierd way made debconf’s frontend think that postinst was finished (it probably closed the inherited file descriptors that were opened by one or more of NAV’s daemons).
Today I found a solution in the debconf specification (why didn’t I read this in detail earlier?). Debconf have a function called stop, which let the frontend know we are done talking to it, and it will stop waiting for the daemons to close those file descriptors (if this really was the problem). Yay! 