First, please excuse me andignore my faults: I'm french.
My mac i bought in 2013(1,4 GHz Intel Core i5/8 Go 1600 MHz DDR3Intel HD Graphics 5000 1536 Mo)currently works with OS X El Capitan. Pixelmator is up to date (3.4Version"Twist").
When I add a vintage effect on my pic, a bright band appears. The vintage effect doesn't cover the all pic. Check out the picture below.
Thanks for you help.