I had the same thing happen with WL810 even with fermcap when my stirplate threw the bar overnight. I would use it and not worry about it. This is one reason I always try to overshoot my approximate number when doing starters. Also, because there is always a bit left in my flask and jars I keep it in.
I do 4L starters in a 5L flask all the time and using 4 drops of fermcap, and now that I have my stir plate dialed in perfectly, it works. If you don't get much of a vortex on your plate you can still get a krausen like that, the vortex will suck it down. Before I had my stirplate fixed, I wouldn't get a big vortex in 4L and had issues like these even when I doubled the fermcap amount.
If you aren't getting a strong vortex, try shimming under your flask with something small and building it up. That fixed my problem.