This affects 1.5.2 MC by the way, for some reason I couldn't put that in the versions tab so apologies for that.

Essentially what I put in summary, in a nutshell the outlines of all textures have become visible leaving a thin line which shows the skybox. Please see attached image of stone with the thin lines around each block. This has also affected non-block textures such as flowers, leaving lines above the block in a similar fashion

It's not much of a bug I know, more an irritating glitch. Thanks