I too for the first time had some unusual white stuff on the inside of my mouth, on the corners. Seemed different from the normal build up and also the build up that get's white when it's wet from e.g. saliva, as it was quite hard to get off (I tried it once or twice to see what structure / texture it had). The "white line", if I wanted to remove it, is usually wiped away very easily.
I noticed those white patches a few days after I got the results from a swab / culture which showed that I have Candida in my mouth and on my lips. So I believe that those white patches COULD have been caused by Candida. They also went away after starting a course of an antifungal suspension (similar to Nystatin).
Maybe you would want to get a swap / culture done as well.