[LMP]

A possibility - other than fuel spillage - is that the car ran for quite a time with a much lower fuel pressure. THe computer has adapted (from the reading of the O2 sensor) and has adjusted injector opening time accordingly. THese values have adapted the "open loop " short and long time parameters . These values are kept and used when engine has not entered CLOSED LOOP operation.
Normally, it should detect the "rich" condition dependent of the higher pressure now available and then reduce the injector ON time...but for this the engine must enter the CLOSED LOOP condition, where the O2 values are infact read and used to readjust the parameters.
Closed loop is attained only after engine has attained normal operating temperature...and requires some time to adapt.
If you do only short treks, it will take sometime to adjust.
If you do one long run, it should recover to previous values...unless the O2 readings are not accurate ,( damaged O2 sensor.)