Why "BackingStore" doesn't work with the "Xrender" extensions ?

Issue

• Unable to use BackingStore with the Xrender extension in custom application.

Example:

• In sample test program try to draw two transparent rectangles in a window and move any other window to cover the window and then expose it, this will damage the two rectangles.
• There are no problems if XRender calls not being used in program.
• On RHEL 5.5, The issue will be gone if drawing a normal rectangle before or after. However this trick does not work on RHEL 6.4.
• This issue was observed on RHEL 5.5 and RHEL 6.4.