Sometime, the wooden post disappear when I look at it,
and I can't modify it with the Engineer's Hammer, nothing happen when I click.
Or others stranges things happen like that:

Modpack: FTB Revelation
Immersive Engineering version: 0.12-84

Can I ask what the hell vanilla is doing that this happens?

They glitch out like that when put at y-level 63/64.
Just put them a bit higher.

Can't help it, vanilla bug.