this setting has no effect if DATA SOURCE is set to (local)
and it means DATA SOURCE, not any other field,
and you have set not to local but "DDE"
Database settings -> Data Source: DDE
Your database is PLUGIN DRIVEN (In your case DDE).
ANY plugin driven database is subject to "Number of bars" setting. When database is plugin driven, it uses "Number of bars" setting in File->Database Settings as the upper limit of bars per symbol.