I made a cute little dolphin quilt that will forever to referred to as the wonky dolphin quilt. My 1/4 inch seam is more like what ever width my presser foot is, it's pretty close. Well that works if you are using the same machine/foot to make the entire quilt. I didn't. I forced my blocks together, stretching some here, pleating a little there. I sent it off the charity LA, and she promptly returned it to me as a complete mess and "please don't do that again." It wouldn't lay flat at all. It had little mountains and valleys when you laid it flat. Another quilter took it over as a challenge and fixed it. I don't know what she did, I know she didn't take it completely apart.
So don't mix your seam sizes. Be consistant.