To demonstrate this, I created a grid of tiled background objects. The image I used was 32 x 32 pixels and the grid was made of tiled backgrounds at 64 x 64 pixels each. From what I could tell, there is a 1 pixel (or so) gap between each tile.
Since I don't know the implementation behind construct and behind cocoonjs I can't say for certain who's fault this is, but I'd hope that since this affects construct that scirra will take this bug on and liaise with ludei if this is a fault in their canvas implementation.
Also, I placed a ring of tiled background objects around the level. So they are not visible and do not lie inside the level, they simply surround the level. In chrome, the object outside the level bleeds into the frame by 1 pixel.
We need pixel perfect rendering please.
To save you the time of reproducing the cocoonjs bug:
I'd make it a link but I can't be trusted :P