While messing around making mob farms (I was playing in hard) a spider spawned near where I was working with the invisibility effect on it. I approached it and there was a separate group of spiders that had entered the same chunk as the invisible spider and the texture of the spider proceeded to bug out, allowing me to see all the textures of the spider on every side. I tried doing the same with Endermen, and mobs that retain textures when invisible will cause non invisible versions of one of those mobs to not render the texture correctly. This worked from spider to enderman, enderman to enderman, enderman to spider, and spider to spider. I have some screenshots showing this, also it tends to be random... sometimes it happens and sometimes it doesnt... I'm not 100% sure what the criteria are for it to occur.