While doing some testing I noticed that vpp ends in a strange state when doing a specific stats dance:

1. want_interface_simple_stats
2. disconnect
3. connect
4. want_stats
5. disconnect
6. connect
7. want_interface_simple_stats

            Now what happens is that vpp sends combined interface counters, though only simple were requested. It seems that using ~0 as item in various stats registration contexts, while reusing code for simple/combined counters doesn't play well if combined. If after 5.) you put a breakpoint on do_combined_interface_counters(), you'll see that it's called regularly even though the client is gone now...

            This was seen with VAPI unit test and doing an explicit want_stats with enable_disable=0 workarounds the issue. I've added such fix, but I still think this should be fixed.