Hi,
If you have a look in your Transformer model, click on a data source and then the general tab you will notice that there is a item called "Sets the current period".
The way I personally handle it is to create a seperate source called Current period with a calculated item that is set to todays date and make sure that the "Sets the current period" is checked. On all other data source feeds I uncheck the Set current period.
Rgds
Rob