Well I'm inclined to agree with Smidijack. And if it's a very fast sequence, practice should help.
I'm amused that you seem to think this must be a bug in the software, simply because it doesn't do what you want it to.
Until you made the comment about not being able to lift your finger off the key fast enough I was puzzled over why you'd have this problem. The only thing I could think of would be if you wanted to trigger more than one event from the same keyboard - for example playing a note and holding it for longer than the duration of the sequence.
It's worth talking abiout that anyway, as it may be useful for somebody reading this -
If you wanted to do that you could assign the sequencer on/off to a control knob via midi, and just turn off the sequencer by hand while continuing to hold the note. I've never needed to do that, but I've turned the sequencer on and off via Midi assignment on its own and it works fine.
The usual way to deal with speed issues with the original Modular was to record the synth and then alter the speed afterwards. That was a work-around for the original sluggish envelopes on the modular, among other things, if I recall rightly.
If you can't get the keying right, maybe you could record the sequence at half speed and then double it to the speed you want when you've got the passage you want to record.
Or if you need to play this live, you might be better doing what I've just suggested and then sampling the result, instead of playing it direct from the MMV.