I replaced the stock rounds on my Yamaha RBX170 with Labella DTF-M a few months ago. While tightening the E string during installation a piece of the plastic nut broke off from where the E string lays, on out to the edge. It would have played that way fine (the E string stayed put), but I had planned on getting a professional setup right away so my luther went ahead and replaced it with a new nut.
In hindsight, maybe I should have had the luther put the new flats on. It's likely that the new strings were larger in diameter than the rounds were and the nut's string space might have needed a wider filing to have prevented the nut from breaking in the first place. Flats in general, and especially the Labella's, are notorious for having higher tension.
I absolutely love the tone and feel of these strings.