I have this too for my Messaging Folder. I used to resize every time to get rid of the line because it bugged me, but I noticed that soon after getting rid of that line, the phone would act funny and I'd have to soft reset. The "phone acting funny" is not scientific or anything like that, and I can't prove it...but that's the conclusion I came to inside my head and I'm sticking to it. Anyway, yes, I do get that same exact line and I'm thinking maybe it does it to folders that have many apps in it? My Message folder has by far the most apps stored in it and it's the only folder that has that line. I've since just left it and it doesn't bother me too much anymore. Please go into Feedback Hub to report this...I did.