--- preseed.xml-old	2012-08-24 17:32:39.151894889 +0200
+++ preseed.xml	2012-08-24 17:33:24.503758761 +0200
@@ -1106,6 +1106,7 @@
 d-i partman-md/device_remove_md boolean true
 # And the same goes for the confirmation to write the lvm partitions.
 d-i partman-lvm/confirm boolean true
+d-i partman-lvm/confirm_nooverwrite boolean true
 
 # You can choose one of the three predefined partitioning recipes:
 # - atomic: all files in one partition