This is totally expected. When you change the resolution, you change it effectively for everything, including layers that may be fed into effects to drive parameters. It doesn't just scale the output, it realyl changes the native sampling steps. You have to work at 100% size and full res for predictable results in such cases.
I've found out that deleting all the cache and memory works.
guess this was a cache issue. you know you could click that "Currect Answer" button so us geeks won't rush to your post trying to help or maybe we could learn something by seeing what was the current answer. just think about it. no rush.