WPF TabContorl not refreshing after hidden for a period of time

I have a WPF application which has one MainWindow (most space was occupied by a TabControl). It gets displayed by a user click on a menu item in Excel. Closing the MainWindow will only set Visibility = Visibility.Hidden so next time ShowDialog called, it will be instant.

However, I have found that after being "hidden" for few hours, the TabControl on MainWindow freezes. All the items/controls within the tab control are still clickable (will react the clicking as well), but the TabControl UI is notredene开发者_JAVA百科ring. Items outside the TabControl worked OK.

If I recreate the window object, it will be fine but I am still wondering why this is happening.

Thank you very much