I can't reproduce any problem. There is no repeat effect on the background here, which makes sense because your .capx has "Clear background" set to "Yes". Even if I set it to "No", it still renders correctly because there is an opaque layer at the bottom. I do not understand what the layer color has to do with this. Did you submit the correct .capx?
I'm sure this I've linked the correct capx file.
I've tried this out on my Windows 7 machine and I do not get this issue on any browser.
On my Windows 8.1 machine, Chrome was the only one that worked as expected.
On Internet Explorer 11, the background flickers between black and the set colour (in this screenshot it should be white) .[attachment=0:123yozj8][/attachment:123yozj8]
On Firefox 30, the repeating effect occurs (as seen near the top) and theirs a white area around the sprite where it should be transparent. [attachment=1:123yozj8][/attachment:123yozj8]