Volume voices auto reduct

In Options > Audio Switcher. I tick enable, normalize, max amplication: 1000%
Why audio auto reduct when i watching video? If i seek a bar. It will normal again.
Same when i tick regain volume, it will auto reduct, but max volume not 1000%, it just between min 150% max 500%.
I have read http://codecguide.com/faq_playback_issues.htm#item17 for this problem, and got same problem.
And i try change master volume above 100%, it make noise.
Can make volume of voices fixed?

If you want fixed volume, then you should disable volume normalize. Instead you should only enable the Mixer and boost the volume of the Center channel in the Mixer settings. A good value should be 142%. Much higher might give quality problems.