Comment 3 for bug 1056381

The failing assert is a new one which was not present in precise:

    assert (!screen_specific_private[type]);

The type passed in is PRIVATE_PIXMAP, and:

static const Bool screen_specific_private[PRIVATE_LAST] = {
    [PRIVATE_SCREEN] = FALSE,
    [PRIVATE_CLIENT] = FALSE,
    [PRIVATE_WINDOW] = TRUE,
    [PRIVATE_PIXMAP] = TRUE,
    [PRIVATE_GC] = TRUE,
    [PRIVATE_CURSOR] = FALSE,
    [PRIVATE_COLORMAP] = FALSE,
    [PRIVATE_DEVICE] = FALSE,
    [PRIVATE_EXTENSION] = FALSE,
    [PRIVATE_SELECTION] = FALSE,
    [PRIVATE_PROPERTY] = FALSE,
    [PRIVATE_PICTURE] = TRUE,
    [PRIVATE_GLYPHSET] = FALSE,
};

i.e. screen_specific_private[PRIVATE_PIXMAP] is true- whatever that means.