* More AA6YQ comments below
+ There's clearly a defect lurking here; thanks for reporting theIt is likely in the data N1MM+ emits in the UDP broadcast. Any way to check the *TIME* in the four QSOs N1MM has logged? I don't believe DXKeeper considers the "Exchange1"/"SRX_STRING" data in its duplicate checking routine (only date/time/call/band/frequency/mode) thus the four N1MM+ "QSO" records would each need to have unique times. If any two QSOs were recorded with the same time to the second, the second QSO record would probably be ignored as a duplicate by DXKeeper.
* Only if duplicate checking were enabled on the Main window's "Import QSOs" tab, which is not recommended given the performance penalty.