I tried the previous version of the Trail Short (the 3.5") in a Size Small and returned them because they immediately rolled up into my crotch. I decided to give the updated 4" version a try and was pleasantly surprised that the fit had improved. I will say that the leg openings definitely still creep up while running, when I am running faster (7:00 pace) they definitely end up with in an inch of my bikini line, just at the top of my inner thigh pooch, but they don't roll at least, and to be honest, I find them comfortable sitting there, since the laser cut seems don't irritate anything. I do wish they didn't ride up quite so much, I think the leg openings could be tighter to help them stay down and grip. I have pretty large, muscular thighs and still think they could be tighter. Overall, I think if you are fine with the shorts sitting higher on your leg, these are still very comfortable and the pocket layout is too great to pass up.
I also think Janji needs to update their size charts. I am solidly an XS according to their size chart - I have a 26 inch waist and 36 inch hips, 5'7" and 130 lb - but I have always worn a Small in all Janji shorts. I ordered these in both an XS and a Small and while I liked the tighter leg openings on the XS, the waist band was too tight. I kept the Small. I wish I could have the XS size leg openings on the Small to give them more grip.
UPDATE after running a marathon in them: I loved these shorts, they are my new marathon race shorts. Didn't even notice them at all during the race, no adjusting or pulling up or down or anything! And perfect for carrying all of my gels and phone and id and hotel key, etc! Will be purchasing more, please don't change them and make them in more fun colors and prints!