[cairo] User code triggers some inner Cairo assert

[Sebastien Kramm]

Hello,
This is my first post here.

For some application, I am writing a wrapper over basic drawing stuff with cairo, 
and the corresponding images are displayed into Gtk+2 windows. It ""kinda works"". 
However, one of my samples triggers an internal cairo assert, and I really don't see 
how to fix this. The log is:

demo1: /build/buildd/cairo-1.10.2/src/cairo.c:173: _cairo_error: Assertion `(status 
!= CAIRO_STATUS_SUCCESS && status <= CAIRO_STATUS_LAST_STATUS)' failed.

Something in my code is probably doing something really bad, but I don't know what.
FIY, its a C++ app, that is calling a set of C functions that are wrappers over the 
drawing back-end library (Cairo) and window managment (Gtk+2).
I only use a small subset of the Cairo functions, drawing on images is done with the 
classical pattern (creating a cairo_t* with cairo_create(), drawing, then release the 
object).

 From error message, I seem to be using 1.10 version (plateform is Ubuntu 12.04). I 
tried to upgrade to 1.12, but the classical:
   sudo apt-get install libcairo2-dev
as suggested by:
   http://www.cairographics.org/download/
tells me that:
   "libcairo2-dev is already the newest version"
(although this seems to be false).

I checked the corresponding code via:
   http://cgit.freedesktop.org/cairo/tree/src/cairo.c?id=1.10.2
and the assert is in some function:
    cairo_status_t _cairo_error (cairo_status_t status)
that my code does NOT call.

My knowledge of Cairo is very limited, so I'm stuck. Any advice on how to move on 
would be appreciated.