Topband: K3 Noise Blanker problem?

[Larry - K1UO]

Hello all..    This AM on 160 meters there was a station CQing on 1.820.6 with a fundamental freq signal strength of S9 on my K3.  I also found (with the NB on) that I could hear him Q5 but very weak on 1.810.6 and the same S 0 reading but perfectly Q5  on 1.830.6.  I turned the noise blanker off and of course the images disappeared.  Is this a know problem when using the NB or is this just with my radio after a recent factory alignment?   I have had a K3 for years and never noticed anything like that before but then again this AM was very quiet on 160M and I had the NB on because I could hear a distant tick tick of an electric fence.