Symmetry not working after creating sub-assembly.

Step 1. Add 6 fuel adapters to the bottom of a fuel tank.
Step 2. Add an an engine to the fuel adapters. All 6 adapters should get an engine.
Step 3. Drag an engine and create a sub-assembly.
Step 4. Once it is done the symmetry wont work until the engine is removed and then re-added.