I noticed the issue first on TechReborn, but I'm pretty sure other RebornCore mods have this issue. It's a bit difficult to see given the resolution, but the transform for the RebornCore block is not the same as the transform for the dirt block, which causes those blocks to look very strange next to vanilla or other mod blocks.

Shown in the screenshot is a thermal generator, a dirt block and a Quark andesite brick. The dirt block and the andesite brick have the same transform, but the thermal generator is rotated slightly incorrectly.

It might get fixed