I'm having this issue too when i export CocoonJS, it shows the lines in the grid. Try to reproduce:
1-Create a Tile Background
2-Fill it with black colour and set resize 64 x 64
3-Cover tile background on layout area
4-Make it fade behavior, then fade in 2 seconds and fade out 2 seconds.
5-Export to cocoonJS
6-Try it on your device, it appears the edges can't be ajusted on opacity.
Besides, if you have no time to reproduce on these steps, here is a .capxhttp://dl.dropbox.com/u/76227787/blacklinestile.capx