Why do the controls in the document re-initialize when I switch the document tab?

[nasterhe]

TestDock.zip
Please see the attached sample project. Through debugging, I can find that whenever I switch the document tab, StartPageView is initialized, I don't know where I set it wrong, please help me, thank you.

[wieslawsoltes]

You need to enable caching.

[nasterhe]

You need to enable caching.
Thank you for your reply. I've decided to use TabControl instead of DocmentDock, but I'll still use your Tool for each TabItem, thank you for your dedication.