today nzbget crashed several times when a download failed and nzbDrone tried to redownload the file via nzbget. I contacted the developer of nzbget and he answered with the following:
Indeed, I see in the log, that the request was from NzbDrone.
I can now reproduce the crash in NZBGet and will fix it. Nonetheless NzbDrone should not use command “HistoryReturn”, especially not for items not having any parked files. NzbDrone should use “HistoryRedownload” instead.