Low Pass Filter Problem

[supersynth]

Take an Init preset, change the filter mode from bypass to Low Pass, turn cutoff knob to the maximum. That still doesn't sound like the full saw wave should sound, it's still cutting some of the highs. In fact, if you change back to bypass you can clearly tell the difference. That's not meant to happen, in every synth if you apply a LP filter and you turn the cutoff knob all up, it's the same as using no filter at all.

How am I supposed to get around this? It makes it impossible for me to do a lot of things, like automating the filter from minimum to maximum, cause I can never reach that maximum.

Also, why does turning the Filter Control cutoff knob to the max make the sound quieter?