I create a valid cairo context in c (which I can use w/o errors) for an xcb surface. Then I wrap it via the Pycairo_CAPI like this:

pcr = PycairoContext_FromContext(cr, NULL, NULL);

In Python I do
pcr.rectangle(0,0,10,10)
pcr.fill()

The fill operation triggers the following backtrace. I followed the execution path in pycairo and it doesn't seem to use anything unusual, meaning the same commands in c do not segfault.

(gdb) bt
#0  0xb7e98a1c in memcpy () from /lib/i686/cmov/libc.so.6
#1  0xb7aea285 in _get_image_surface (surface=0xb789f338, interest_rect=<value optimized out>, image_out=0xbfd12484, image_rect=0xbfd12520) at cairo-xcb-surface.c:412
#2  0xb7aea63a in _cairo_xcb_surface_acquire_dest_image (abstract_surface=0x8157258, interest_rect=0xbfd12514, image_out=0xbfd1251c, image_rect_out=0xbfd12520, image_extra=0xbfd12528) at cairo-xcb-surface.c:654
#3  0xb7abbbe0 in _cairo_surface_acquire_dest_image (surface=0x3374, interest_rect=0xbfd12514, image_out=0xbfd1251c, image_rect=0xbfd12520, image_extra=0xbfd12528) at cairo-surface.c:968
#4  0xb7abda38 in _fallback_init (state=0xbfd12510, dst=0x27100, x=13172, y=0, width=30, height=30) at cairo-surface-fallback.c:78
#5  0xb7abdd23 in _cairo_surface_fallback_fill_rectangles (surface=0x8157258, op=CAIRO_OPERATOR_OVER, color=0xbfd1310c, rects=0xbfd1259c, num_rects=1) at cairo-surface-fallback.c:1159
#6  0xb7abc0b1 in _cairo_surface_fill_rectangles (surface=0x8157258, op=CAIRO_OPERATOR_OVER, color=0xbfd1310c, rects=0xbfd1259c, num_rects=1) at cairo-surface.c:1314
#7  0xb7abc299 in _cairo_surface_fill_region (surface=0x8157258, op=CAIRO_OPERATOR_OVER, color=0xbfd1310c, region=0xbfd12f78) at cairo-surface.c:1262
#8  0xb7abf0ce in _clip_and_composite_trapezoids (src=<value optimized out>, op=<value optimized out>, dst=0x8157258, traps=0xbfd12fe4, clip=0x0, antialias=CAIRO_ANTIALIAS_DEFAULT)
    at cairo-surface-fallback.c:620
#9  0xb7abf35a in _cairo_surface_fallback_fill (surface=0x8157258, op=CAIRO_OPERATOR_OVER, source=0xbfd130b4, path=0x81a1a30, fill_rule=CAIRO_FILL_RULE_WINDING, tolerance=0.10000000000000001, 
    antialias=CAIRO_ANTIALIAS_DEFAULT) at cairo-surface-fallback.c:907
#10 0xb7abca68 in _cairo_surface_fill (surface=0x8157258, op=CAIRO_OPERATOR_OVER, source=0xbfd1319c, path=0x81a1a30, fill_rule=CAIRO_FILL_RULE_WINDING, tolerance=0.10000000000000001, 
    antialias=CAIRO_ANTIALIAS_DEFAULT) at cairo-surface.c:1456
#11 0xb7aafd33 in _cairo_gstate_fill (gstate=0x81a18e0, path=0x81a1a30) at cairo-gstate.c:1044
#12 0xb7aa87bc in *INT_cairo_fill_preserve (cr=0x81a18c0) at cairo.c:2098
#13 0xb7aa87e2 in cairo_fill (cr=0x81a18c0) at cairo.c:2074
#14 0xb7fc3d35 in ?? () from /usr/lib/python2.4/site-packages/cairo/_cairo.so
#15 0x081a18c0 in ?? ()
#16 0xb7dc394c in ?? ()
#17 0xb7fcbfa0 in ?? () from /usr/lib/python2.4/site-packages/cairo/_cairo.so
#18 0xb7e22040 in ?? ()
#19 0xb7e22040 in ?? ()
#20 0x00000000 in ?? ()