Well it seems that the logic behind Pickup Machine tempo recalc (sequencer running, OT is master clock ) is as follows:
1: Qrec and Qpl obey master track lenght like @Open_Mike noticed so if your master track is 64 steps, rec/play actions will be quantized to a 64/128/192/256/320 grid
2: Tempo recalc on the other hand takes the next coming value on a 16/32/64/128/256/512 etc grid as a reference.
Example: with master track =64, a PU recording stop action at step 135 will stop recording at step 192 and tempo will be recalculated as if the recording was 256 steps long as shown in the video I posted above (mind this: it will not choose 128 which is closer to 135 than 256!!).
In other words, if we want quantized PU recordings, of an undefined lenght, that do not change the tempo, we only have the choice of 64/128/256/512 etc amount of steps but we need to initiate a stop action during the last master track cycle. (BTW Track scale doesn’t matter, only Master Track scale does).
For master track =64:
target=64: action stop anywhere will do
target=128: action stop between 64 and 128
target=256: action stop between 192 and 256
target=512: action stop between 448 and 512
target=1024: action stop between 960 and 1024
Hence, a fully quantized Pickup recording of 96, 192 or 320 beats is not possible.
This is not a bug, but I qualify this as a design flaw: we have two different reference grids, AND a weird rounding choice has been made.
This explains most of the “Pick-up’s are unpredictable” issues. They are very consistent! But we are musicians, not mathematiciens…