Switching on and off layers too much slowwww

Hello everybody!
I will try to explain my problem:
i started a project with blender 2.62 and i used to put object in different layers; so switching on and off layers was really useful and i dit that a lot of times.
The problem is with version 2 .63: i opened the same file but the time to switch(off on, only first time) layer increased really too much; at example when i activate one layer more instead of taking 2 seconds(with 2.62) to be displayed on viewport it take more than 10… there is some bug behind or there are compatibily issues with bmesh?
Sorry for my maybe bad english:D