Yes, it is 845.

By 'entered properly, I mean the manner in which notes are expected to be entered in the Notation view (in editable mode) I select the first 16th of the first beat and then complete the bar according to the melody.

If I now select the Soloist track and enter my note in the first sixteenth again, I am unable to reverse this using Ctrl-Z or 'Undo Insert Note', these operations are completely ignored. Well that's not strictly true, when I Ctl-Z in the Soloist it does not. I can select the note and delete it though. Interestingly, if I Ctl-Z in the soloist, even though it does not reverse the operation, if I now go to Edit, I am told that there is no note to delete.