I worked on my game a bit last night and found the following:
Tiled backgrounds have to be a perfect square otherwise the tiling doesn't work correctly.
If I take a very small right angled triangle and stretch it a lot to fill up an area, then the transparent edges show some sort of fill.
Also, when overlaying multiple images, sometimes it draws strange outline on the transparent sides. I'll play around with the pixel size and rounding.
Even though I stop a certain music track, it keeps playing.
I will get some screenshots later - off to my day job.