sfPropelDatabase which inherit sfDatabase now have __construct() constructor that will call initialize with empty array.
Looking at generated config_databases.yml.php, first step is a new sfPropelDatabase created and second step, it's initialized.
On first step initialize called with empty parameters and connection named propel.
On second step initialize called with parameters and connection name based on configuration.
Typically, this won't fall if only one connection defined in configuration and named propel by default (second step call to initialize replace the first call).
But, with multiple datasource defined, on next datasource, when sfPropelDatabase created it may replace the existing datasource named propel which previously initialized.