This depends on the terms of your contract.
Most often, a RE company will include a clause that says "if you rent this property within 180 days of expiration to a propsect that is intoduced to the property while under contract" the listing agency AND the selling agency is due and owing a commission (i.e., 100% of the total initial agreemnt). This should be explained to you in full, but I find that most often it is not 100% clear to sellers/landlords.
This clause becomes null and void once u list with another agency.
I recently assisted a landlord who contaced me via Trulia with the same situation. Feel free to give me a call to discuss further.
Love and Peace,
Francesca, Realtor, ePro