Sometimes skeletons spawn by two.

[split goblet]

I seen at least 3 times, how they spawn by two next to each other in neighbor blocks, I assume they supposed to be alone?

[rich notch]

this is intentional, there's a 5% chance for skeletons to spawn another one right next to it and another 5% chance for that second skeleton to spawn another one too

[olive gust]

it is intentional

[covert blade]

indeed