Georgy,
I think what you have discovered (300-3000Hz Bandpass) is the cause of problems with nearby strong CW signals desensitizing reception of weaker signal in the narrow filter. Either AGC is applied to this wider bandwidth before the narrow filtering or the strong signal overloads the radio. It is too bad that the 300-3000 filter isn't made narrower corresponding to the mode: CW, RTTY, PSK31.
Gary
W9TD
Gary