
On the right I used a rotor to try the same and on the middle I used a piston. The large hydrogen thruster on the left is built on a hinge and has a merge block on one of its sides. When you try the same with a rotor or a hinge they don't merge, as seen on the first screenshot.

When two merge blocks (one static, the other on a subgrid) are brought close to each other with a piston they merge as intended. So I tried with a rotor and a piston (built on the same grid as the hinge) to see if the problem happened too, and it happened only with the rotor. But no matter how many times I tried, the merge blocks never merged.

As I was building a small grid cargo shuttle I wanted to add hinge-mounted large hydrogen thrusters on it and lock them in place with merge blocks once they had moved to the desired orientation.
