patch adapted from upstream:
http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/commit/?id=e8cb0b721e6ea251f85c799ca0563bfa59a2d37c

Signed-off-by: Bernd Kuhls <berndkuhls@hotmail.com>

diff -uNr xf86-video-ati-6.14.6.org/src/radeon_driver.c xf86-video-ati-6.14.6/src/radeon_driver.c
--- xf86-video-ati-6.14.6.org/src/radeon_driver.c	2012-06-25 10:19:41.000000000 +0200
+++ xf86-video-ati-6.14.6/src/radeon_driver.c	2014-03-29 17:27:54.712440644 +0100
@@ -3753,10 +3753,6 @@
     RADEONInitMemMapRegisters(pScrn, info->ModeReg, info);
     RADEONRestoreMemMapRegisters(pScrn, info->ModeReg);
 
-    /* Backing store setup */
-    xf86DrvMsgVerb(pScrn->scrnIndex, X_INFO, RADEON_LOGLEVEL_DEBUG,
-		   "Initializing backing store\n");
-    miInitializeBackingStore(pScreen);
     xf86SetBackingStore(pScreen);
 
     /* DRI finalisation */
diff -uNr xf86-video-ati-6.14.6.org/src/radeon_kms.c xf86-video-ati-6.14.6/src/radeon_kms.c
--- xf86-video-ati-6.14.6.org/src/radeon_kms.c	2012-06-29 15:45:35.000000000 +0200
+++ xf86-video-ati-6.14.6/src/radeon_kms.c	2014-03-29 17:28:02.328340925 +0100
@@ -1036,10 +1036,6 @@
 #endif
 
     pScrn->vtSema = TRUE;
-    /* Backing store setup */
-    xf86DrvMsgVerb(pScrn->scrnIndex, X_INFO, RADEON_LOGLEVEL_DEBUG,
-		   "Initializing backing store\n");
-    miInitializeBackingStore(pScreen);
     xf86SetBackingStore(pScreen);