Shadows for entities are not rendered as a single circle, but rather as a sheet of multiple circles (reminiscent of a pattern from the 1960s). I first noticed this issue in 1.10.2, but it seems to persist in 1.11.2 as well. I'm not sure if it's an LWJGL issue or an issue with Mesa or perhaps even a driver issue. I can't say for sure when this appeared as I haven't been playing Minecraft actively enough to notice.