Comment 2 for bug 1040768

StacktraceTop:
 memmove (__len=<optimized out>, __src=0x7f751f491a10, __dest=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:58
 pixman_op (new_reg=new_reg@entry=0x2287ef8, reg1=reg1@entry=0x2287ef8, reg2=reg2@entry=0x7f7504004518, overlap_func=overlap_func@entry=0x7f751f468c20 <pixman_region_union_o>, append_non1=append_non1@entry=1, append_non2=append_non2@entry=1, overlap=overlap@entry=0x7f7512b2e6fc) at ../../pixman/pixman-region.c:1004
 pixman_region32_union (new_reg=new_reg@entry=0x2287ef8, reg1=reg1@entry=0x2287ef8, reg2=0x7f7504004518) at ../../pixman/pixman-region.c:1453
 INT_cairo_region_union (dst=0x2287ef0, other=<optimized out>) at /build/buildd/cairo-1.12.2/src/cairo-region.c:681
 impl_window_add_update_area (region=0x7f7504004510, impl_window=0x2428360) at /build/buildd/gtk+3.0-3.5.12/./gdk/gdkwindow.c:4362