When looking at a block at an angle the breaking animation appears to glow.
Environment
Windows 8.1, most recent Java, running as a non-steam game via steam. 2 monitors, game is running in fullscreen on only the primary monitor, which is 1920x1080. FOV is 100. Fancy graphics
Also this is duplicating my report (MC-58276), I must admit that your report has the better screenshot 😉