Here is a sample of generated code with Vala 0.12.1 (it's OK):

static gboolean completion_provider_real_match (GtkSourceCompletionProvider* base, GtkSourceCompletionContext* context) {
        /* ... */

        GtkTextIter _tmp0_ = {0};
        GtkTextIter iter;
        GtkTextBuffer* _tmp1_ = NULL;
        GtkTextBuffer* _tmp2_;
        GtkTextBuffer* buf;

        /* ... */

        iter = _tmp0_;
        gtk_source_completion_context_get_iter (context, &iter);
        _tmp1_ = gtk_text_iter_get_buffer (&iter);

        /* ... */
}


And here is the same sample but generated with Vala 0.13.4:

static gboolean completion_provider_real_match (GtkSourceCompletionProvider* base, GtkSourceCompletionContext* context) {
        /* ... */
        
        GtkTextIter _tmp0_ = {0};
        GtkTextIter iter;
        GtkSourceCompletionContext* _tmp1_;
        GtkTextIter _tmp2_;
        GtkTextBuffer* _tmp3_ = NULL;
        
        /* ... */
        
        iter = _tmp0_;
        _tmp1_ = context;
        _tmp2_ = iter;
        gtk_source_completion_context_get_iter (_tmp1_, &_tmp2_);
        _tmp3_ = gtk_text_iter_get_buffer (&iter);
        
        /* ... */
}

There is a segfault with this code. To get the iter, Vala 0.13 assign the value to _tmp2_, but there is no "iter = _tmp2_;" afterwards. So when the next line try to get the value of "iter", there is a problem.

I didn't try to write a minimal Vala code where this bug happens, I hope that the above samples are sufficient.