I receive some hundred CRON Job messages a day some times a message is received and deleted on the server. The filter moves the message to the destination folder. With the next manual receive this message is received again, shown for a just a short moment in the inbox and moved to the destination folder as a duplicate. This happens again and again so there are dozens copies ijhn the destination folder. This stops when I deactivate the filter criteria. In this case the message is received once an no further copies are received.
This bug has only been reported for versions before 4.14, which have been unsupported for at least two years now. Can anyone tell if this bug still present? If noone confirms this bug for a Framework-based version of kmail2 (version 5.0 or later, as part of KDE Applications 15.12 or later), it gets closed in about three months.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.