It must of been assimilation.
WHen you use a tablet there is a chance that any other stat on your weapon, white and blue ones can get changed up or down or assimilates but stays the same anyway. It is random it can change 1%, or go up to like 80%, or go down to 0%. It is completely luck based.
For a list of what tablets does what, go here
http://sro.mmosite.com/alchemy/tablets.shtml