Serialization test fails during construction

[historic_bruno]

This is consistently reproducible for me:

1. Load a map in Atlas, Acropolis 1 works
2. Start simulation test
3. Build a field
4. When construction finishes, delete the field
5. Build a mill

The serialization test fails while approaching the mill foundation. Sometimes there is no difference in the debug state logs, sometimes there is one local entity difference (which shouldn't affect the serialization).