You can also test with midi loopback : received Notes On are recorded with the right timing. 32 notes max per bar with scale x2. I don’t play that fast. 
The problem is also with notes overlapping. You can erase previously recorded notes with long notes. I’d love an overdub option…
Yup. This is one of those things that became a lot more noticeable in my experience with the arrival of Syntakt. Specifically when using mod keys for things like long retriggers. It also makes them extremely difficult to record in one take. I usually have to do a couple takes with undo actions. Would prefer the option to toggle that potentially, and let length behave like it would with manual placements.
How would this overdub work when the seq records monophonic
Maybe like the high low last note priority setting on a mono synth, except it would be previous rec trig/last trig priority setting then your playing for example long notes could get interrupted by seq trigs instead of the opposite as it is now
They way it is I use it as a feature when jamming like a punch in note replace to slowly evolve a melodic seq when recording. Or playing changes over the top, not recording- for example with short decay no sustain playing in New notes for a change up and holding them to mute out the seq notes and then releasing to reveal the original seq again
Yes real overdub requires polyphony. For monophonic tracks I’d like to be able to record new notes without erasing previous ones.
I find a bar of pre-roll metronome helps a lot, especially if I rehearse during it.