I avoid this problem by not trimming the quilt before adding binding. Instead of cutting, I mark the cutting line. (I use a regular Sharpie permanent pen because I want the marking highly visible but do not want any chance of it bleeding.) I align the raw edge of the binding with this line to sew it on. After the binding is sewn on one side, I trim the quilt sandwich to fit. (Be careful not to cut through the binding at the corners! That would create holes.)
It sounds counter-intuitive, but I found that this approach eliminates the issue I used to have with having an occasional edge flip on me when sewing on the binding. Also, it lets me adjust the depth of the batting so it fills the binding the way I want it.
If you prefer to baste the edges, I recommend doing this basting before trimming. Being able to pin to the right of the machine basting line helps keep everything even.