Leakage current in in-line mains filters
Figure 1. A mains filter. Notice the two Y capacitors. Source: Elliot Sound Systems.


The current through the Y capacitors will be proportional to the voltage across them. 
Note that the left CY is between neutral and earth while the right one is between live and earth.
Since the neutral is "neutralised" by bonding it to earth at the local transformer or building meter point there should be no voltage difference between N and E. Hence there should be no current in the N-E capacitor.
Both capacitors are required in case of L-N reversal due to use of non-polarised plugs or mis-wiring. The neutral capacitor may also be required to shunt high frequency harmonics or noise to earth as L1 will tend to block them.



  Are they same when it comes to leakage current as a parameter?


No.