@Override
	public void setDefaultValue(RegisterValue registerValue, Address start, Address end) {
		if (!start.getAddressSpace().equals(end.getAddressSpace())) {
			throw new IllegalArgumentException(
				"start and end address must be within the same address space");
		}
		Register baseRegister = registerValue.getRegister().getBaseRegister();
		RegisterValueStore store = defaultRegisterValueMap.get(baseRegister);
		if (store == null) {
			RangeMapAdapter adapter = new InMemoryRangeMapAdapter();
			store = new RegisterValueStore(baseRegister, adapter, false);
			defaultRegisterValueMap.put(baseRegister, store);
		}
		store.setValue(start, end, registerValue);
		invalidateReadCache();
	}
if the address is in an overlay and we are getting the default value, then get the default
value from the base space, not the overlay space.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/util/AbstractStoredProgramContext.java