Weired rendering with double-buffered parent and themes

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Which steps will reproduce the problem?
 1. Create a form with a THTMLViewer and a TXPManifest.
 2. For the form, set DoubleBuffered:=TRUE.
 3. In OnCreate, fill the THTMLViewer with text, so that a scrollbar
    must appear.
 4. Run the program with a Windows Aero theme active.

What is the expected output?
 - The scrollbar should ALWAYS be visible, no matter where the
   mouse cursor is positioned.

What do you see instead?
 - By default, the scrollbar is visible (fine).
 - By moving the mouse, the scrollbar VANISHES when the mouse
   enters or leaves the scrollbar region, and slowly fades in
   again.
 - When the vertical scrollbar vanishes, the HTML text from the
   left side of the THTMLViewer is duplicated at the place where
   the scrollbar SHOULD be.

This problem does NOT appear when
 - using Windows Classic Mode,
 - the TXPManifest is thrown out or
 - the THTMLViewer is put on any parent with DoubleBuffered:=FALSE.

Which version of the product are you using?
 - HtmlViewer113-r306
   (the error also appeared in version 112-r254)

Which compiler version are you using?
 - Delphi XE2, 32bit

On which operating system?
 - Windows 7, 64bit

Original issue reported on code.google.com by weidner....@t-online.de on 24 Oct 2012 at 9:08

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[deleted comment]

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Also observed under Windows 7 32 bit and Windows 8 64 bit

Original comment by leonardo.herrera on 3 May 2013 at 8:02

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Issue 249 has been merged into this issue.

Original comment by OrphanCat on 18 Jun 2013 at 8:24

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Original comment by OrphanCat on 18 Jun 2013 at 8:26

• Changed title: Weired rendering with double-buffered parent and themes
• Changed state: Accepted