Java HotSpot Virtual Machine

Hi everyone!
I launched my application using for GARBAGE COLLECTION these options:

-Xmx512m -Xms512m -XX:MaxNewSize=24m -XX:NewSize=24m -XX:SurvivorRatio=2 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC

SurvivorRatio is 2, so I expect two survivors spaces of 6 MB each one and an eden space of 12 MB. GC log files (PrintGC options used) surprised me: Eden space is almost all NewSize and two Survivors spaces are only 64KB each one.
If I don't use -XX:+UseConcMarkSweepGC -XX:+UseParNewGC options, spaces have the values expected (12 MB Eden, 6 MB each one survivors space).

Why does JVM behave in this way?

Thank you very much in advance.

Diego