9-patch: seams visible even when "Exact" selected

Link to .capx file (required!):

snugsound.com/dev/c2-9-patch-wrapping/9-patch-wrapping.capx

Steps to reproduce:

1. Create a 9-patch object using attached image (Source-image.png); set all margins to 16, "Edges" and "Fill" to "Tile" and "Seams" to "Exact"

2. Add a few instances to a new layout

3. Run the project

Source image:

<img src="http://snugsound.com/dev/c2-9-patch-wrapping/Source-image.PNG" border="0" />

Source image (to show 16px grid, and transparency):

<img src="http://snugsound.com/dev/c2-9-patch-wrapping/Source-image-with-16px-grid.PNG" border="0" />

Observed result:

Some blocks have visible seams

<img src="http://snugsound.com/dev/c2-9-patch-wrapping/9-patch-wrapping.PNG" border="0" />

Expected result:

No seams should be visible since "Exact" was specified

Browsers affected:

Chrome: yes

Firefox: yes

Internet Explorer: N/A (not targeting IE)

Operating system & service pack:

Windows 7 SP1 32-bit

Construct 2 version:

C2 R132 32-bit

Closing, this is the top row of pixels wrapping back down to the bottom. Add a row of transparent pixels to the top of the image.

Can you elaborate? From my perspective there should be nothing below the bottom "margin" area. Why is it wrapping? Only the "tiled" area (the middle 16, in the zoomed-in image above) should be wrapping, unless I'm misunderstanding the intended behaviour of the 9-patch?

Adding a row of transparent pixels is fine for scenery, but for objects with the "Solid" behaviour it then results in a gap for floor collisions, since there are no collisions masks for 9-patches.

'Letterbox scale' allows floating-point scaling, which means sub-pixel rendering can occur. Sub-pixel rendering at the bottom of a tiled image means the top of the image wraps back again, as if the image was repeating again below. To avoid that, either use a row of transparent pixels at the top, or set point sampling, pixel rounding and letterbox integer scale to ensure sub-pixel rendering never happens.

Thanks for clarifying