Gentoo with old Advanced Micro Devices, Inc. [AMD/ATI] RV710 [Radeon HD 4350/4550]
Slightly broken: media-gfx/blender-2.79b-r1
Short description of error
When zooming in as much as possible on a texture in the UV/Image Editor, there seems to be a pixel border at y≈235.994 instead of exactly at y=236 like I'd expect.
Assuming the error was due to 32-bit floating-point rounding, the border coordinates should have at least 2 more digits of precision.