I have an article in QRP Quarterly about varying the tuning rate according to how fast you are turning the encoder. I have mine defaulted to 100Hz but when you turn it fast, the rate is 5 KHz. Give it a try.
The 49er is not especially selective -- the passband is broad and the front-end can be over-loaded quite easily. This is why Jack designed the BCI filter; could it be, the CW operator you heard is in your neighborhood? Also, if you haven't, try going to 1KHz resolution tuning so you move more quickly up or down the band.
jjpurdum