When Ted has to drive Jake's girlfriend home from the party, the reason he has to drive the Rolls Royce is because Ted can't drive a standard. But when Jake pulls up the next morning in his Porsche 944 you can see that when he engages the transmission, it is an automatic.
There is no slip-up with this part of the movie! The garage scene proves this because the reason that Ted has to drive the Rolls Royce is that he CAN'T drive a stick (as Jake says to Ted - his Porsche is a stick). This is also proven the next morning when Ted and Caroline are in the parking lot and Jake sees them. He puts his car into first gear and parks! There are no inconsistencies with this part of the movie!