Nothing to do with pitch-bend (which can however suffer from a similar phenomenon). A "steppy" filter sweep is caused by digital quantisation of the cutoff frequency - at high resonance levels a slow sweep may be heard to move up or down its range in discrete steps rather than smoothly, something that a purely analogue-controlled filter will never do (unless you have a modular synth that will allow you to do this deliberately!) On most modern analogue synths, the cutoff frequency is quantised in this way to allow overall digital control of the analogue circuitry. The trade-off is worthwhile in most cases, as MIDI control of filter parameters would be impractical without it.