Slurs forced above staff when extending over more than one measure
For as long as I can see, we have tried to implement a rule in slur layout where "long" slurs are forced above the staff. This isn't inherently a bad thing, but our definition of "long" is bad - "anything over one measure in duration" is how we implement it. In reality, this is a pretty subjective determination and we shouldn't make it automatically. Or at least, we should have a more sensible threshold, one based on length of the slur in sp units, not on duration in fractions.