Automated rocket takes off without engine

So, I had this  rocket with the following modules: Steam engine, solid fuel thruster, cargo bay and command capsule.

I attached an automation cable in the command capsule so it would take off immediately once all conditions were met.

But my solid fuel thruster was melting my thermium conveyor rail so, as the rocket was being fueled I ordered the duplicants to deconstruct the cargo bay so I could rebuild the rocket.

Once they deconstructed the cargo bay the rocket took off with only the solid fuel thruster and the command capsule.

The Optimistic Cosmos.sav